Dispersed storage re-dispersion method based on a failure

ABSTRACT

A method begins by identifying a storage unit of a set of storage units within a dispersed storage system as being likely to fail. The method continues by determining an approach for minimizing rebuilding the encoded data slices that are stored on an identified storage unit in an event of a failure of the identified storage unit. The approach is at least one approach option from a list of approach options that includes fostering new encoded data slices, replicating existing encoded data slices, and re-dispersing existing encoded data slices. The method continues by implementing the approach regarding the identified storage unit and when the identified storage unit fails, retrieving the encoded data slices that were stored on the identified storage unit based on the approach.

CROSS REFERENCE TO RELATED PATENTS

The present U.S. Utility Patent Application claims priority pursuant to35 U.S.C. §120 as a continuation of U.S. Utility application Ser. No.13/021,510, entitled “DISPERSED STORAGE NETWORK SLICE NAMEVERIFICATION”, filed Feb. 4, 2011, (now issued U.S. Pat. No. 9,047,218),which claims priority pursuant to 35 U.S.C. §119(e) to U.S. ProvisionalApplication No. 61/327,921, entitled “SYSTEM ACCESS AND DATA INTEGRITYVERIFICATION IN A DISPERSED STORAGE SYSTEM”, filed Apr. 26, 2010, bothof which are hereby incorporated herein by reference in their entiretyand made part of the present U.S. Utility Patent Application for allpurposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not Applicable

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

This invention relates generally to computing systems and moreparticularly to data storage solutions within such computing systems.

2. Description of Related Art

Computers are known to communicate, process, and store data. Suchcomputers range from wireless smart phones to data centers that supportmillions of web searches, stock trades, or on-line purchases every day.In general, a computing system generates data and/or manipulates datafrom one form into another. For instance, an image sensor of thecomputing system generates raw picture data and, using an imagecompression program (e.g., JPEG, MPEG, etc.), the computing systemmanipulates the raw picture data into a standardized compressed image.

With continued advances in processing speed and communication speed,computers are capable of processing real time multimedia data forapplications ranging from simple voice communications to streaming highdefinition video. As such, general-purpose information appliances arereplacing purpose-built communications devices (e.g., a telephone). Forexample, smart phones can support telephony communications but they arealso capable of text messaging and accessing the internet to performfunctions including email, web browsing, remote applications access, andmedia communications (e.g., telephony voice, image transfer, musicfiles, video files, real time video streaming. etc.).

Each type of computer is constructed and operates in accordance with oneor more communication, processing, and storage standards. As a result ofstandardization and with advances in technology, more and moreinformation content is being converted into digital formats. Forexample, more digital cameras are now being sold than film cameras, thusproducing more digital pictures. As another example, web-basedprogramming is becoming an alternative to over the air televisionbroadcasts and/or cable broadcasts. As further examples, papers, books,video entertainment, home video, etc., are now being stored digitally,which increases the demand on the storage function of computers.

A typical computer storage system includes one or more memory devicesaligned with the needs of the various operational aspects of thecomputer's processing and communication functions. Generally, theimmediacy of access dictates what type of memory device is used. Forexample, random access memory (RAM) memory can be accessed in any randomorder with a constant response time, thus it is typically used for cachememory and main memory. By contrast, memory device technologies thatrequire physical movement such as magnetic disks, tapes, and opticaldiscs, have a variable response time as the physical movement can takelonger than the data transfer, thus they are typically used forsecondary memory (e.g., hard drive, backup memory, etc.).

A computer's storage system will be compliant with one or more computerstorage standards that include, but are not limited to, network filesystem (NFS), flash file system (FFS), disk file system (DFS), smallcomputer system interface (SCSI), internet small computer systeminterface (iSCSI), file transfer protocol (FTP), and web-baseddistributed authoring and versioning (WebDAV). These standards specifythe data storage format (e.g., files, data objects, data blocks,directories, etc.) and interfacing between the computer's processingfunction and its storage system, which is a primary function of thecomputer's memory controller.

Despite the standardization of the computer and its storage system,memory devices fail; especially commercial grade memory devices thatutilize technologies incorporating physical movement (e.g., a discdrive). For example, it is fairly common for a disc drive to routinelysuffer from bit level corruption and to completely fail after threeyears of use. One solution is to utilize a higher-grade disc drive,which adds significant cost to a computer.

Another solution is to utilize multiple levels of redundant disc drivesto replicate the data into two or more copies. One such redundant driveapproach is called redundant array of independent discs (RAID). In aRAID device, a RAID controller adds parity data to the original databefore storing it across the array. The parity data is calculated fromthe original data such that the failure of a disc will not result in theloss of the original data. For example, RAID 5 uses three discs toprotect data from the failure of a single disc. The parity data, andassociated redundancy overhead data, reduces the storage capacity ofthree independent discs by one third (e.g., n−1=capacity). RAID 6 canrecover from a loss of two discs and requires a minimum of four discswith a storage capacity of n−2.

While RAID addresses the memory device failure issue, it is not withoutits own failure issues that affect its effectiveness, efficiency andsecurity. For instance, as more discs are added to the array, theprobability of a disc failure increases, which increases the demand formaintenance. For example, when a disc fails, it needs to be manuallyreplaced before another disc fails and the data stored in the RAIDdevice is lost. To reduce the risk of data loss, data on a RAID deviceis typically copied on to one or more other RAID devices. While thisaddresses the loss of data issue, it raises a security issue sincemultiple copies of data are available, which increases the chances ofunauthorized access. Further, as the amount of data being stored grows,the overhead of RAID devices becomes a non-trivial efficiency issue.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a schematic block diagram of an embodiment of a computingsystem in accordance with the invention;

FIG. 2 is a schematic block diagram of an embodiment of a computing corein accordance with the invention;

FIG. 3 is a schematic block diagram of an embodiment of a distributedstorage processing unit in accordance with the invention;

FIG. 4 is a schematic block diagram of an embodiment of a grid module inaccordance with the invention;

FIG. 5 is a diagram of an example embodiment of error coded data slicecreation in accordance with the invention;

FIG. 6 is a flowchart illustrating an example of generating integrityinformation in accordance with the invention;

FIG. 7 is a flowchart illustrating an example of verifying sliceintegrity in accordance with the invention;

FIG. 8 is a diagram of an example of a hash tree structure in accordancewith the invention;

FIG. 9 is a flowchart illustrating an example of identifying sliceerrors in accordance with the invention;

FIG. 10A is a schematic block diagram of another embodiment of acomputing system in accordance with the invention;

FIG. 10B is a schematic block diagram of another embodiment of acomputing system in accordance with the invention;

FIG. 11A is a flowchart illustrating an example of storing data inaccordance with the invention;

FIG. 11B is a flowchart illustrating an example of migrating data inaccordance with the invention;

FIG. 12A is a schematic block diagram of another embodiment of acomputing system in accordance with the invention;

FIG. 12B is a schematic block diagram of another embodiment of acomputing system in accordance with the invention;

FIG. 13 is a flowchart illustrating an example of utilizing a dispersedstorage unit in accordance with the invention;

FIG. 14A is a schematic block diagram of another embodiment of acomputing system in accordance with the invention;

FIG. 14B is a schematic block diagram of another embodiment of acomputing system in accordance with the invention;

FIG. 15A is a flowchart illustrating an example of re-dispersing anencoded data slice in accordance with the invention;

FIG. 15B is a flowchart illustrating another example of migrating datain accordance with the invention;

FIG. 16A is a flowchart illustrating an example of replicating anencoded data slice in accordance with the invention;

FIG. 16B is a flowchart illustrating another example of migrating datain accordance with the invention;

FIG. 17 is a schematic block diagram of another embodiment of acomputing system in accordance with the invention;

FIG. 18 is a flowchart illustrating an example of archiving data inaccordance with the invention;

FIG. 19 is a flowchart illustrating another example of storing data inaccordance with the invention;

FIG. 20 is a flowchart illustrating an example of retrieving data inaccordance with the invention;

FIG. 21 is a flowchart illustrating another example of retrieving datain accordance with the invention;

FIG. 22 is a diagram illustrating an example of encoded data sliceaccess sequences in accordance with the invention;

FIG. 23 is a flowchart illustrating another example of retrieving datain accordance with the invention; and

FIG. 24 is a flowchart illustrating an example of verifying a retrievalsequence in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic block diagram of a computing system 10 thatincludes one or more of a first type of user devices 12, one or more ofa second type of user devices 14, at least one distributed storage (DS)processing unit 16, at least one DS managing unit 18, at least onestorage integrity processing unit 20, and a distributed storage network(DSN) memory 22 coupled via a network 24. The network 24 may include oneor more wireless and/or wire lined communication systems; one or moreprivate intranet systems and/or public internet systems; and/or one ormore local area networks (LAN) and/or wide area networks (WAN).

The DSN memory 22 includes a plurality of distributed storage (DS) units36 for storing data of the system. Each of the DS units 36 includes aprocessing module and memory and may be located at a geographicallydifferent site than the other DS units (e.g., one in Chicago, one inMilwaukee, etc.). The processing module may be a single processingdevice or a plurality of processing devices. Such a processing devicemay be a microprocessor, micro-controller, digital signal processor,microcomputer, central processing unit, field programmable gate array,programmable logic device, state machine, logic circuitry, analogcircuitry, digital circuitry, and/or any device that manipulates signals(analog and/or digital) based on hard coding of the circuitry and/oroperational instructions. The processing module may have an associatedmemory and/or memory element, which may be a single memory device, aplurality of memory devices, and/or embedded circuitry of the processingmodule. Such a memory device may be a read-only memory, random accessmemory, volatile memory, non-volatile memory, static memory, dynamicmemory, flash memory, cache memory, and/or any device that storesdigital information. Note that if the processing module includes morethan one processing device, the processing devices may be centrallylocated (e.g., directly coupled together via a wired and/or wireless busstructure) or may be distributedly located (e.g., cloud computing viaindirect coupling via a local area network and/or a wide area network).Further note that when the processing module implements one or more ofits functions via a state machine, analog circuitry, digital circuitry,and/or logic circuitry, the memory and/or memory element storing thecorresponding operational instructions may be embedded within, orexternal to, the circuitry comprising the state machine, analogcircuitry, digital circuitry, and/or logic circuitry. Still further notethat, the memory element stores, and the processing module executes,hard coded and/or operational instructions corresponding to at leastsome of the steps and/or functions illustrated in FIGS. 1-24.

Each of the user devices 12-14, the DS processing unit 16, the DSmanaging unit 18, and the storage integrity processing unit 20 may be aportable computing device (e.g., a social networking device, a gamingdevice, a cell phone, a smart phone, a personal digital assistant, adigital music player, a digital video player, a laptop computer, ahandheld computer, a video game controller, and/or any other portabledevice that includes a computing core) and/or a fixed computing device(e.g., a personal computer, a computer server, a cable set-top box, asatellite receiver, a television set, a printer, a fax machine, homeentertainment equipment, a video game console, and/or any type of homeor office computing equipment). Such a portable or fixed computingdevice includes a computing core 26 and one or more interfaces 30, 32,and/or 33. An embodiment of the computing core 26 will be described withreference to FIG. 2.

With respect to the interfaces, each of the interfaces 30, 32, and 33includes software and/or hardware to support one or more communicationlinks via the network 24 and/or directly. For example, interface 30supports a communication link (wired, wireless, direct, via a LAN, viathe network 24, etc.) between the first type of user device 14 and theDS processing unit 16. As another example, DSN interface 32 supports aplurality of communication links via the network 24 between the DSNmemory 22 and the DS processing unit 16, the first type of user device12, and/or the storage integrity processing unit 20. As yet anotherexample, interface 33 supports a communication link between the DSmanaging unit 18 and any one of the other devices and/or units 12, 14,16, 20, and/or 22 via the network 24.

In general and with respect to data storage, the computing system 10supports three primary functions: distributed network data storagemanagement, distributed data storage and retrieval, and data storageintegrity verification. In accordance with these three primaryfunctions, data can be distributedly stored in a plurality of physicallydifferent locations and subsequently retrieved in a reliable and securemanner regardless of failures of individual storage devices, failures ofnetwork equipment, the duration of storage, the amount of data beingstored, attempts at hacking the data, etc.

The DS managing unit 18 performs distributed network data storagemanagement functions, which include establishing distributed datastorage parameters, performing network operations, performing networkadministration, and/or performing network maintenance. The DS managingunit 18 establishes the distributed data storage parameters (e.g.,allocation of virtual DSN memory space, distributed storage parameters,security parameters, billing information, user profile information,etc.) for one or more of the user devices 12-14 (e.g., established forindividual devices, established for a user group of devices, establishedfor public access by the user devices, etc.). For example, the DSmanaging unit 18 coordinates the creation of a vault (e.g., a virtualmemory block) within the DSN memory 22 for a user device (for a group ofdevices, or for public access). The DS managing unit 18 also determinesthe distributed data storage parameters for the vault. In particular,the DS managing unit 18 determines a number of slices (e.g., the numberthat a data segment of a data file and/or data block is partitioned intofor distributed storage) and a read threshold value (e.g., the minimumnumber of slices required to reconstruct the data segment).

As another example, the DS managing unit 18 creates and stores, locallyor within the DSN memory 22, user profile information. The user profileinformation includes one or more of authentication information,permissions, and/or the security parameters. The security parameters mayinclude one or more of encryption/decryption scheme, one or moreencryption keys, key generation scheme, and data encoding/decodingscheme.

As yet another example, the DS managing unit 18 creates billinginformation for a particular user, user group, vault access, publicvault access, etc. For instance, the DS managing unit 18 tracks thenumber of times a user accesses a private vault and/or public vaults,which can be used to generate a per-access bill. In another instance,the DS managing unit 18 tracks the amount of data stored and/orretrieved by a user device and/or a user group, which can be used togenerate a per-data-amount bill.

The DS managing unit 18 also performs network operations, networkadministration, and/or network maintenance. As at least part ofperforming the network operations and/or administration, the DS managingunit 18 monitors performance of the devices and/or units of thecomputing system 10 for potential failures, determines the devices'and/or units' activation status, determines the devices' and/or units'loading, and any other system level operation that affects theperformance level of the computing system 10. For example, the DSmanaging unit 18 receives and aggregates network management alarms,alerts, errors, status information, performance information, andmessages from the devices 12-14 and/or the units 16, 20, 22. Forexample, the DS managing unit 18 receives a simple network managementprotocol (SNMP) message regarding the status of the DS processing unit16.

The DS managing unit 18 performs the network maintenance by identifyingequipment within the computing system 10 that needs replacing,upgrading, repairing, and/or expanding. For example, the DS managingunit 18 determines that the DSN memory 22 needs more DS units 36 or thatone or more of the DS units 36 needs updating.

The second primary function (i.e., distributed data storage andretrieval) begins and ends with a user device 12-14. For instance, if asecond type of user device 14 has a data file 38 and/or data block 40 tostore in the DSN memory 22, it sends the data file 38 and/or data block40 to the DS processing unit 16 via its interface 30. As will bedescribed in greater detail with reference to FIG. 2, the interface 30functions to mimic a conventional operating system (OS) file systeminterface (e.g., network file system (NFS), flash file system (FFS),disk file system (DFS), file transfer protocol (FTP), web-baseddistributed authoring and versioning (WebDAV), etc.) and/or a blockmemory interface (e.g., small computer system interface (SCSI), internetsmall computer system interface (iSCSI), etc.). In addition, theinterface 30 may attach a user identification code (ID) to the data file38 and/or data block 40.

The DS processing unit 16 receives the data file 38 and/or data block 40via its interface 30 and performs a distributed storage (DS) processthereon (e.g., an error coding dispersal storage function). The DSprocessing 34 begins by partitioning the data file 38 and/or data block40 into one or more data segments, which is represented as Y datasegments. For example, the DS processing 34 may partition the data file38 and/or data block 40 into a fixed byte size segment (e.g., 2¹ to2^(n) bytes, where n=>2) or a variable byte size (e.g., change byte sizefrom segment to segment, or from groups of segments to groups ofsegments, etc.).

For each of the Y data segments, the DS processing 34 error encodes(e.g., forward error correction (FEC), information dispersal algorithm,or error correction coding) and slices (or slices then error encodes)the data segment into a plurality of error coded (EC) data slices 42-48,which is represented as X slices per data segment. The number of slices(X) per segment, which corresponds to a number of pillars n, is set inaccordance with the distributed data storage parameters and the errorcoding scheme. For example, if a Reed-Solomon (or other FEC scheme) isused in an n/k system, then a data segment is divided into n slices,where k number of slices is needed to reconstruct the original data(i.e., k is the threshold). As a few specific examples, the n/k factormay be 5/3; 6/4; 8/6; 8/5; 16/10.

For each EC slice 42-48, the DS processing unit 16 creates a uniqueslice name and appends it to the corresponding EC slice 42-48. The slicename includes universal DSN memory addressing routing information (e.g.,virtual memory addresses in the DSN memory 22) and user-specificinformation (e.g., user ID, file name, data block identifier, etc.).

The DS processing unit 16 transmits the plurality of EC slices 42-48 toa plurality of DS units 36 of the DSN memory 22 via the DSN interface 32and the network 24. The DSN interface 32 formats each of the slices fortransmission via the network 24. For example, the DSN interface 32 mayutilize an internet protocol (e.g., TCP/IP, etc.) to packetize the ECslices 42-48 for transmission via the network 24.

The number of DS units 36 receiving the EC slices 42-48 is dependent onthe distributed data storage parameters established by the DS managingunit 18. For example, the DS managing unit 18 may indicate that eachslice is to be stored in a different DS unit 36. As another example, theDS managing unit 18 may indicate that like slice numbers of differentdata segments are to be stored in the same DS unit 36. For example, thefirst slice of each of the data segments is to be stored in a first DSunit 36, the second slice of each of the data segments is to be storedin a second DS unit 36, etc. In this manner, the data is encoded anddistributedly stored at physically diverse locations to improve datastorage integrity and security. Further examples of encoding the datasegments will be provided with reference to one or more of FIGS. 2-24.

Each DS unit 36 that receives an EC slice 42-48 for storage translatesthe virtual DSN memory address of the slice into a local physicaladdress for storage. Accordingly, each DS unit 36 maintains a virtual tophysical memory mapping to assist in the storage and retrieval of data.

The first type of user device 12 performs a similar function to storedata in the DSN memory 22 with the exception that it includes the DSprocessing. As such, the user device 12 encodes and slices the data fileand/or data block it has to store. The device then transmits the slices11 to the DSN memory via its DSN interface 32 and the network 24.

For a second type of user device 14 to retrieve a data file or datablock from memory, it issues a read command via its interface 30 to theDS processing unit 16. The DS processing unit 16 performs the DSprocessing 34 to identify the DS units 36 storing the slices of the datafile and/or data block based on the read command. The DS processing unit16 may also communicate with the DS managing unit 18 to verify that theuser device 14 is authorized to access the requested data.

Assuming that the user device is authorized to access the requesteddata, the DS processing unit 16 issues slice read commands to at least athreshold number of the DS units 36 storing the requested data (e.g., toat least 10 DS units for a 16/10 error coding scheme). Each of the DSunits 36 receiving the slice read command, verifies the command,accesses its virtual to physical memory mapping, retrieves the requestedslice, or slices, and transmits it to the DS processing unit 16.

Once the DS processing unit 16 has received a read threshold number ofslices for a data segment, it performs an error decoding function andde-slicing to reconstruct the data segment. When Y number of datasegments has been reconstructed, the DS processing unit 16 provides thedata file 38 and/or data block 40 to the user device 14. Note that thefirst type of user device 12 performs a similar process to retrieve adata file and/or data block.

The storage integrity processing unit 20 performs the third primaryfunction of data storage integrity verification. In general, the storageintegrity processing unit 20 periodically retrieves slices 45, and/orslice names, of a data file or data block of a user device to verifythat one or more slices have not been corrupted or lost (e.g., the DSunit failed). The retrieval process mimics the read process previouslydescribed.

If the storage integrity processing unit 20 determines that one or moreslices is corrupted or lost, it rebuilds the corrupted or lost slice(s)in accordance with the error coding scheme. The storage integrityprocessing unit 20 stores the rebuilt slice, or slices, in theappropriate DS unit(s) 36 in a manner that mimics the write processpreviously described.

FIG. 2 is a schematic block diagram of an embodiment of a computing core26 that includes a processing module 50, a memory controller 52, mainmemory 54, a video graphics processing unit 55, an input/output (10)controller 56, a peripheral component interconnect (PCI) interface 58,an 10 interface 60, at least one 10 device interface module 62, a readonly memory (ROM) basic input output system (BIOS) 64, and one or morememory interface modules. The memory interface module(s) includes one ormore of a universal serial bus (USB) interface module 66, a host busadapter (HBA) interface module 68, a network interface module 70, aflash interface module 72, a hard drive interface module 74, and a DSNinterface module 76. Note the DSN interface module 76 and/or the networkinterface module 70 may function as the interface 30 of the user device14 of FIG. 1. Further note that the 10 device interface module 62 and/orthe memory interface modules may be collectively or individuallyreferred to as 10 ports.

The processing module 50 may be a single processing device or aplurality of processing devices. Such a processing device may be amicroprocessor, micro-controller, digital signal processor,microcomputer, central processing unit, field programmable gate array,programmable logic device, state machine, logic circuitry, analogcircuitry, digital circuitry, and/or any device that manipulates signals(analog and/or digital) based on hard coding of the circuitry and/oroperational instructions. The processing module 50 may have anassociated memory and/or memory element, which may be a single memorydevice, a plurality of memory devices, and/or embedded circuitry of theprocessing module 50. Such a memory device may be a read-only memory,random access memory, volatile memory, non-volatile memory, staticmemory, dynamic memory, flash memory, cache memory, and/or any devicethat stores digital information. Note that if the processing module 50includes more than one processing device, the processing devices may becentrally located (e.g., directly coupled together via a wired and/orwireless bus structure) or may be distributedly located (e.g., cloudcomputing via indirect coupling via a local area network and/or a widearea network). Further note that when the processing module 50implements one or more of its functions via a state machine, analogcircuitry, digital circuitry, and/or logic circuitry, the memory and/ormemory element storing the corresponding operational instructions may beembedded within, or external to, the circuitry comprising the statemachine, analog circuitry, digital circuitry, and/or logic circuitry.Still further note that, the memory element stores, and the processingmodule 50 executes, hard coded and/or operational instructionscorresponding to at least some of the steps and/or functions illustratedin FIGS. 1-24.

FIG. 3 is a schematic block diagram of an embodiment of a dispersedstorage (DS) processing module 34 of user device 12 and/or of the DSprocessing unit 16. The DS processing module 34 includes a gatewaymodule 78, an access module 80, a grid module 82, and a storage module84. The DS processing module 34 may also include an interface 30 and theDSnet interface 32 or the interfaces 68 and/or 70 may be part of userdevice 12 or of the DS processing unit 16. The DS processing module 34may further include a bypass/feedback path between the storage module 84to the gateway module 78. Note that the modules 78-84 of the DSprocessing module 34 may be in a single unit or distributed acrossmultiple units.

In an example of storing data, the gateway module 78 receives anincoming data object that includes a user ID field 86, an object namefield 88, and the data object field 40 and may also receivecorresponding information that includes a process identifier (e.g., aninternal process/application ID), metadata, a file system directory, ablock number, a transaction message, a user device identity (ID), a dataobject identifier, a source name, and/or user information. The gatewaymodule 78 authenticates the user associated with the data object byverifying the user ID 86 with the DS managing unit 18 and/or anotherauthenticating unit.

When the user is authenticated, the gateway module 78 obtains userinformation from the DS management unit 18, the user device, and/or theother authenticating unit. The user information includes a vaultidentifier, operational parameters, and user attributes (e.g., userdata, billing information, etc.). A vault identifier identifies a vault,which is a virtual memory space that maps to a set of DS storage units36. For example, vault 1 (i.e., user 1's DSN memory space) includeseight DS storage units (X=8 wide) and vault 2 (i.e., user 2's DSN memoryspace) includes sixteen DS storage units (X=16 wide). The operationalparameters may include an error coding algorithm, the width n (number ofpillars X or slices per segment for this vault), a read threshold T, awrite threshold, an encryption algorithm, a slicing parameter, acompression algorithm, an integrity check method, caching settings,parallelism settings, and/or other parameters that may be used to accessthe DSN memory layer.

The gateway module 78 uses the user information to assign a source name35 to the data. For instance, the gateway module 78 determines thesource name 35 of the data object 40 based on the vault identifier andthe data object. For example, the source name may contain a fileidentifier (ID), a vault generation number, a reserved field, and avault identifier (ID). As another example, the gateway module 78 maygenerate the file ID based on a hash function of the data object 40.Note that the gateway module 78 may also perform message conversion,protocol conversion, electrical conversion, optical conversion, accesscontrol, user identification, user information retrieval, trafficmonitoring, statistics generation, configuration, management, and/orsource name determination.

The access module 80 receives the data object 40 and creates a series ofdata segments 1 through Y 90-92 in accordance with a data storageprotocol (e.g., file storage system, a block storage system, and/or anaggregated block storage system). The number of segments Y may be chosenor randomly assigned based on a selected segment size and the size ofthe data object. For example, if the number of segments is chosen to bea fixed number, then the size of the segments varies as a function ofthe size of the data object. For instance, if the data object is animage file of 4,194,304 eight bit bytes (e.g., 33,554,432 bits) and thenumber of segments Y=131,072, then each segment is 256 bits or 32 bytes.As another example, if segment size is fixed, then the number ofsegments Y varies based on the size of data object. For instance, if thedata object is an image file of 4,194,304 bytes and the fixed size ofeach segment is 4,096 bytes, then the number of segments Y=1,024. Notethat each segment is associated with the same source name.

The grid module 82 receives the data segments and may manipulate (e.g.,compression, encryption, cyclic redundancy check (CRC), etc.) each ofthe data segments before performing an error coding function of theerror coding dispersal storage function to produce a pre-manipulateddata segment. After manipulating a data segment, if applicable, the gridmodule 82 error encodes (e.g., Reed-Solomon, Convolution encoding,Trellis encoding, etc.) the data segment or manipulated data segmentinto X error coded data slices 42-48.

The value X, or the number of pillars (e.g., X=16), is chosen as aparameter of the error coding dispersal storage function. Otherparameters of the error coding dispersal function include a readthreshold T, a write threshold W, etc. The read threshold (e.g., T=10,when X=16) corresponds to the minimum number of error-free error codeddata slices required to reconstruct the data segment. In other words,the DS processing module 34 can compensate for X−T (e.g., 16−10=6)missing error coded data slices per data segment. The write threshold Wcorresponds to a minimum number of DS storage units that acknowledgeproper storage of their respective data slices before the DS processingmodule indicates proper storage of the encoded data segment. Note thatthe write threshold is greater than or equal to the read threshold for agiven number of pillars (X).

For each data slice of a data segment, the grid module 82 generates aunique slice name 37 and attaches it thereto. The slice name 37 includesa universal routing information field and a vault specific field and maybe 48 bytes (e.g., 24 bytes for each of the universal routinginformation field and the vault specific field). As illustrated, theuniversal routing information field includes a slice index, a vault ID,a vault generation, and a reserved field. The slice index is based onthe pillar number and the vault ID and, as such, is unique for eachpillar (e.g., slices of the same pillar for the same vault for anysegment will share the same slice index). The vault specific fieldincludes a data name, which includes a file ID and a segment number(e.g., a sequential numbering of data segments 1-Y of a simple dataobject or a data block number).

Prior to outputting the error coded data slices of a data segment, thegrid module may perform post-slice manipulation on the slices. Ifenabled, the manipulation includes slice level compression, encryption,CRC, addressing, tagging, and/or other manipulation to improve theeffectiveness of the computing system.

When the error coded data slices of a data segment are ready to beoutputted, the grid module 82 determines which of the DS storage units36 will store the EC data slices based on a dispersed storage memorymapping associated with the user's vault and/or DS storage unitattributes. The DS storage unit attributes may include availability,self-selection, performance history, link speed, link latency,ownership, available DSN memory, domain, cost, a prioritization scheme,a centralized selection message from another source, a lookup table,data ownership, and/or any other factor to optimize the operation of thecomputing system. Note that the number of DS storage units 36 is equalto or greater than the number of pillars (e.g., X) so that no more thanone error coded data slice of the same data segment is stored on thesame DS storage unit 36. Further note that EC data slices of the samepillar number but of different segments (e.g., EC data slice 1 of datasegment 1 and EC data slice 1 of data segment 2) may be stored on thesame or different DS storage units 36.

The storage module 84 performs an integrity check on the outboundencoded data slices and, when successful, identifies a plurality of DSstorage units based on information provided by the grid module 82. Thestorage module 84 then outputs the encoded data slices 1 through X ofeach segment 1 through Y to the DS storage units 36. Each of the DSstorage units 36 stores its EC data slice(s) and maintains a localvirtual DSN address to physical location table to convert the virtualDSN address of the EC data slice(s) into physical storage addresses.

In an example of a read operation, the user device 12 and/or 14 sends aread request to the DS processing unit 16, which authenticates therequest. When the request is authentic, the DS processing unit 16 sendsa read message to each of the DS storage units 36 storing slices of thedata object being read. The slices are received via the DSnet interface32 and processed by the storage module 84, which performs a parity checkand provides the slices to the grid module 82 when the parity check wassuccessful. The grid module 82 decodes the slices in accordance with theerror coding dispersal storage function to reconstruct the data segment.The access module 80 reconstructs the data object from the data segmentsand the gateway module 78 formats the data object for transmission tothe user device.

FIG. 4 is a schematic block diagram of an embodiment of a grid module 82that includes a control unit 73, a pre-slice manipulator 75, an encoder77, a slicer 79, a post-slice manipulator 81, a pre-slice de-manipulator83, a decoder 85, a de-slicer 87, and/or a post-slice de-manipulator 89.Note that the control unit 73 may be partially or completely external tothe grid module 82. For example, the control unit 73 may be part of thecomputing core at a remote location, part of a user device, part of theDS managing unit 18, or distributed amongst one or more DS storageunits.

In an example of a write operation, the pre-slice manipulator 75receives a data segment 90-92 and a write instruction from an authorizeduser device. The pre-slice manipulator 75 determines if pre-manipulationof the data segment 90-92 is required and, if so, what type. Thepre-slice manipulator 75 may make the determination independently orbased on instructions from the control unit 73, where the determinationis based on a computing system-wide predetermination, a table lookup,vault parameters associated with the user identification, the type ofdata, security requirements, available DSN memory, performancerequirements, and/or other metadata.

Once a positive determination is made, the pre-slice manipulator 75manipulates the data segment 90-92 in accordance with the type ofmanipulation. For example, the type of manipulation may be compression(e.g., Lempel-Ziv-Welch, Huffman, Golomb, fractal, wavelet, etc.),signatures (e.g., Digital Signature Algorithm (DSA), Elliptic Curve DSA,Secure Hash Algorithm, etc.), watermarking, tagging, encryption (e.g.,Data Encryption Standard, Advanced Encryption Standard, etc.), addingmetadata (e.g., time/date stamping, user information, file type, etc.),cyclic redundancy check (e.g., CRC32), and/or other data manipulationsto produce the pre-manipulated data segment.

The encoder 77 encodes the pre-manipulated data segment 90-92 using aforward error correction (FEC) encoder (and/or other type of erasurecoding and/or error coding) to produce an encoded data segment 94. Theencoder 77 determines which forward error correction algorithm to usebased on a predetermination associated with the user's vault, a timebased algorithm, user direction, DS managing unit direction, controlunit direction, as a function of the data type, as a function of thedata segment 90-92 metadata, and/or any other factor to determinealgorithm type. The forward error correction algorithm may be Golay,Multidimensional parity, Reed-Solomon, Hamming, Bose Ray ChauduriHocquenghem (BCH), Cauchy-Reed-Solomon, or any other FEC encoder. Notethat the encoder 77 may use a different encoding algorithm for each datasegment 90-92, the same encoding algorithm for the data segments 90-92of a data object, or a combination thereof.

The encoded data segment 94 is of greater size than the data segment90-92 by the overhead rate of the encoding algorithm by a factor of X/T,where X is the width or number of slices, and T is the read threshold.In this regard, the corresponding decoding process can accommodate atmost X-T missing EC data slices and still recreate the data segment90-92. For example, if X=16 and T=10, then the data segment 90-92 willbe recoverable as long as 10 or more EC data slices per segment are notcorrupted.

The slicer 79 transforms the encoded data segment 94 into EC data slicesin accordance with the slicing parameter from the vault for this userand/or data segment 90-92. For example, if the slicing parameter isX=16, then the slicer 79 slices each encoded data segment 94 into 16encoded slices.

The post-slice manipulator 81 performs, if enabled, post-manipulation onthe encoded slices to produce the EC data slices. If enabled, thepost-slice manipulator 81 determines the type of post-manipulation,which may be based on a computing system-wide predetermination,parameters in the vault for this user, a table lookup, the useridentification, the type of data, security requirements, available DSNmemory, performance requirements, control unit directed, and/or othermetadata. Note that the type of post-slice manipulation may includeslice level compression, signatures, encryption, CRC, addressing,watermarking, tagging, adding metadata, and/or other manipulation toimprove the effectiveness of the computing system.

In an example of a read operation, the post-slice de-manipulator 89receives at least a read threshold number of EC data slices and performsthe inverse function of the post-slice manipulator 81 to produce aplurality of encoded slices. The de-slicer 87 de-slices the encodedslices to produce an encoded data segment 94. The decoder 85 performsthe inverse function of the encoder 77 to recapture the data segment90-92. The pre-slice de-manipulator 83 performs the inverse function ofthe pre-slice manipulator 75 to recapture the data segment 90-92.

FIG. 5 is a diagram of an example of slicing an encoded data segment 94by the slicer 79. In this example, the encoded data segment 94 includesthirty-two bits, but may include more or less bits. The slicer 79disperses the bits of the encoded data segment 94 across the EC dataslices in a pattern as shown. As such, each EC data slice does notinclude consecutive bits of the data segment 94 reducing the impact ofconsecutive bit failures on data recovery. For example, if EC data slice2 (which includes bits 1, 5, 9, 13, 17, 25, and 29) is unavailable(e.g., lost, inaccessible, or corrupted), the data segment can bereconstructed from the other EC data slices (e.g., 1, 3 and 4 for a readthreshold of 3 and a width of 4).

FIG. 6 is a flowchart illustrating an example of generating integrityinformation. The method begins at step 102 where a processing modulereceives a store data object message. Such a store data object messagemay include one or more of data, a user identifier (ID), a request, adata ID, a data object name, a data object, a data type indicator, adata object hash, a vault ID, a data size indicator, a priorityindicator, a security indicator, and a performance indicator. The methodcontinues at step 104 where the processing module determines dispersedstorage error coding parameters (e.g., operational parameters) includingone or more of a pillar width, a write threshold, a read threshold, anencoding method, a decoding method, an encryption method, a decryptionmethod, a key, a secret key, a public key, a private key, a keyreference, and an integrity information generation method designator.Such a determination may be based on one or more of information receivedin the store data object message, the user ID, the data ID, a vaultlookup, a list, a command, a message, and a predetermination.

The method continues at step 106 where the processing module dispersedstorage error encodes data to produce a plurality of sets of encodeddata slices in accordance with the dispersed storage error codingparameters. In addition, the processing module determines a plurality ofsets of slice names corresponding to the plurality of sets of encodeddata slices; where a slice name includes one or more of a slice index, avault ID, a generation, an object number, and a segment number. Within aslice name, the slice index indicates a pillar number of a pillar widthassociated with the dispersed storage error coding parameters, the vaultID indicates a storage resource of a storage system common to one ormore user devices, the generation indicates portions of a correspondingvault, the object number is associated with the data ID (e.g., a hash ofthe data ID), and the segment number indicates a segment identifierassociated with one of a plurality of data segments (e.g., the pluralityof data segment constitutes the data, a data file, etc.).

The method continues at step 108 where the processing module determinesintegrity information for the plurality of sets of slice names. Such adetermination may be in accordance with one or more integrity methods.In a first integrity method, the processing module generates individualintegrity information for at least some of the slice names of at leastsome of the plurality of sets of slice names (e.g., at a slice namelevel) and generates the integrity information based on the individualintegrity information. The individual integrity information may begenerated by performing one or more of a hash function, cyclicredundancy check, encryption function, an encrypted digital signaturefunction (e.g., digital signature algorithm (DSA), El Gamal, EllipticCurve DSA, Rivest, Shamir and Adleman (RSA)), and parity check on aslice name of the at least some of the slices names of at least some ofthe plurality of sets of slices names to generate the individualintegrity information. The hash function may include a hashed messageauthentication code (e.g., secure hash algorithm 1 (SHA1), hashedmessage authentication code message digest algorithm 5 (HMAC-MD5)) thatuses a shared key and the encryption function includes an encryptionalgorithm that utilizes a private key, which is paired to a public key.In an example of generating individual integrity information, theprocessing module calculates a hash of at least some of the slice namesand then encrypts the hash in accordance with an encryption method toproduce an encrypted digital signature.

In a second integrity method, the processing module generates setintegrity information for a set of slice names of at least some of theplurality of sets of slice names (e.g., at a set level) and generatesthe integrity information based on the set integrity information. Theset integrity information may be generated by performing one or more ofthe hash function, the cyclic redundancy check, the encryption function,the encrypted digital signature function, and the parity check on theset of slice names of at least some of the plurality of sets of slicenames to generate the set integrity information.

In a third integrity method, the processing module generates pillarintegrity information for a pillar set of slice names of at least someof the plurality of sets of slice names (e.g., at a pillar level) andgenerates the integrity information based on the pillar integrityinformation. The pillar integrity information may be generated byperforming one or more of the hash function, the cyclic redundancycheck, the encryption function, the encrypted digital signaturefunction, and the parity check on the pillar set of slice names of atleast some of the plurality of sets of slice names to generate thepillar integrity information.

In a fourth integrity method, the processing module generates data fileintegrity information for at least some of the plurality of sets ofslice names (e.g., at the data file level) and generates the integrityinformation based on the data file integrity information. The data fileintegrity information may be generated by performing one or more of thehash function, the cyclic redundancy check, the encryption function, theencrypted digital signature function, and the parity check on the atleast some of the plurality of sets of slice names to generate the datafile integrity information.

In a fifth integrity method, the processing module generates combinedintegrity information for at least some of the encoded data slices ofthe plurality of sets of encoded data slices and for at least some ofthe slices names of at least some of the plurality of sets of slicenames and generates the integrity information based on the combinedintegrity information. The combined integrity information includesperforming one or more of the hash function, the cyclic redundancycheck, the encryption function, the encrypted digital signaturefunction, and the parity check on two or more of an encoded data sliceof the at least some of the encoded data slices of the plurality ofencoded data slices, a revision identifier, and an associated slice nameof the at least some of the slice names of the plurality of sets ofslice names to generate the combined integrity information. For example,the processing module performs an RSA encrypted digital signature on acombination of an encoded data slice and an associated slice name togenerate the combined integrity information. As another example, theprocessing module performs a HMAC function on a set of combinations ofencoded data slices and associated slice names name to generate thecombined integrity information. As yet another example, the processingmodule performs a DSA encrypted digital signature on a combination of anencoded data slice, an associated slice name, and an associated revisionidentifier to generate the combined integrity information.

The integrity information may be generated as a combination of thevarious methods. For example, the processing module performs the firstintegrity method, the fourth integrity method, and at least one of thesecond and third integrity methods to generate the integrityinformation.

The method continues at step 110 where the processing module appends theintegrity information to the slice name information to produce appendedslice name information. For example, the processing module appends aHMAC digest to the slice name, revision, and date of a single encodeddata slice. The method continues at step 112 where the processing moduledetermines a dispersed storage (DS) unit storage set. Such adetermination may be based on one or more of information received in thestore data object message, a vault lookup, a list, a command, a message,a predetermination, the dispersed storage error coding parameters,encoded data slices, a dispersed storage network (DSN) memory statusindicator, the slice name information, a virtual DSN address to physicallocation table lookup, and the integrity information. The methodcontinues at step 114 where the processing module sends the plurality ofsets of encoded data slices, the plurality of sets of slice names, andthe integrity information to a DSN memory for storage therein.

FIG. 7 is a flowchart illustrating an example of verifying sliceintegrity, which includes similar steps to FIG. 6. The method beginswith step 116 where a processing module receives a data retrievalrequest. Such a data retrieval request includes one or more of aretrieve data object request, a user identifier (ID), a data objectname, a data ID, a data type indicator, a data object hash, a vault ID,a data size indicator, a priority indicator, a security indicator, and aperformance indicator. The method continues with step 104 of FIG. 6where the processing module determines dispersed storage error codingparameters (e.g., operational parameters) and with step 112 of FIG. 6where the processing module determines a dispersed storage (DS) unitstorage set.

The method continues at step 122 where the processing module determinesa plurality of sets of slice names in accordance with the data retrievalrequest. Such a determination may be based on one or more of the dataID, the user ID, the vault ID, the dispersed storage error codingparameters, and extraction of a data size indicator from a reproduceddata segment. The method continues at step 124 where the processingmodule receives stored integrity information corresponding to the dataretrieval request. For example, the processing module sends one or morestored integrity information request messages to the DS unit storage setand receives the stored integrity information in response, wherein thestored integrity information request messages include at least some ofthe plurality of sets of slice names. Note that the stored integrityinformation and associated encoded data slices were previously stored inthe DS unit storage set.

The method continues at step 126 where the processing module generatesdesired integrity information based on the plurality of sets of slicenames. Such a generation of the desired integrity information may bebased on one or more of the five integrity methods discussed withreference to FIG. 6.

The method continues at step 128 where the processing module receivesencoded data slices. For example, the processing module sends encodeddata slice retrieval messages to the DS unit storage set that includesat least some of the plurality of sets of slice names and receives theencoded data slices in response. The method continues at step 130 wherethe processing module compares the stored integrity information with thedesired integrity information. For example, the processing moduledecrypts the stored integrity information using a public key of apublic-private key pair to produce at least some of a plurality of setsof reconstructed slice names and compares corresponding slices names ofthe plurality of sets of slice names with the at least some of aplurality of sets of reconstructed slice names when the stored integrityinformation includes encrypted slice names (e.g., a digital signature,encrypted slice names) encrypted with a private key of the superpublic-private key pair.

As another example of comparing at step 130, the processing moduledecrypts the stored integrity information using a shared key to producethe at least some of the plurality of sets of reconstructed slice namesand compares corresponding slice names of the plurality of sets of slicenames with the at least some of the plurality of sets of reconstructedslice names when the stored integrity information includes encryptedslice names encrypted with the shared key. The processing modulecompares the stored integrity information directly to the desiredintegrity information when the stored integrity information includesresults of a hash function (e.g., a HMAC).

As yet another example of comparing at step 130, when multiple integritymethods are used (e.g., the fourth integrity and the second or thirdintegrity methods), a higher level comparison is performed first (e.g.,use the forth integrity method). If it is successful, the methodcontinues based on a favorable comparison. If, however, the higher levelcomparison was not successful, a lower level comparison is performed(e.g., the second or third integrity method). For sets of encoded dataslices that the lower level comparison was successful, the methodcontinues based on a favorable comparison. For the sets of encoded dataslices that the lower level comparison was not successful, an error isgenerated or another comparison may be performed based on the individualintegrity information.

As a specific example, an integrity check is initially performed for thedata file. If successful, the method continues with decoding theplurality of sets of encoded data slices to recapture the data file(e.g., step 134). If the data file level integrity check was notsuccessful, then a set level integrity check is performed to identifywhich sets have an error. For each set having an error, an individualencoded slice name integrity check may be performed to identify encodeddata slices having an error. The encoded data slices having an error orsets including slices having an error may be excluded from the decoding(e.g., step 132). Even if encoded data slices have an error, as long asa decode threshold number of encoded data slices per set are available,then the data file can be accurately reproduced.

FIG. 8 is a diagram of an example of a hash tree structure for twopillars of slice storage in a dispersed storage network (DSN) memory. Anindividual hash tree comprises three or more layers including a sourcename and revision list layer 136-138, at least one hash value layer(e.g., hash 12, hash 34), and a root hash layer 140-142. The source nameand revision list layer 136-138 includes entries 1-N. Such entries 1-Nmay include a plurality of blocks 1-4. Note that there may be any numberof blocks. Such blocks may include source names and revision numbers ofencoded data slices stored in a dispersed storage (DS) unit associatedwith a common pillar. A hash value layer includes one or more hashvalues (e.g., hash 12, hash 34), wherein the hash values are calculatedover one or more of the blocks 1-4. For example, hash 12 includes a hashvalue over the source name and revision list entries corresponding toblocks 1 and 2. As another example, hash 34 represents a hash value overthe source name and revision list entries corresponding to blocks 3 and4. The root hash layer 140-142 includes a hash value, wherein the hashvalue is calculated over hash values of a preceding hash value layer.For example, root hash 140-142 includes a hash value over hash 12 andhash 34. Note that any number of hash value layers may be utilized inthe hash tree structure.

The root hash 140 and the root hash 142 yield substantially the samevalue when the same hash tree structure is utilized for each of thepillars and when there are no encoded data slice storage errors (e.g.,missing slices, out of date slices, etc.). Note that a source nameassociated with a first pillar of a set of encoded data slices issubstantially the same as a source name associated with a second pillarof the set of encoded data slices (e.g., same vault identifier (ID),same generation, same object number, and same segment number). Note thata slice error associated with a pillar may be identified by comparing ahash value associated with the pillar to hash values associated with oneor more other pillars.

In an example of slice error identification where a DS unit storage setincludes DS units 1-2 associated with pillars 1-2, each DS unitcalculates an associated hash tree structure creating a plurality ofhash tree structures. Next, a processing module of any one of a DSprocessing unit, a user device, a DS managing unit, a storage integrityprocessing unit, and any DS unit retrieves one or more hash values ofthe plurality of hash tree structures, compare the hash values, anddetermines that a DS unit has slice errors when the comparison indicateshash values that are not substantially the same. The processing modulemay compare hash values traversing similar branches of the plurality ofhash tree structures further and further until reaching a lowest hashvalue layer where those hash values are over entries of the source nameand revision list 136-138 that are not substantially the same. Theprocessing module may also choose a different set of hash values in asame layer to compare when a different previously compared set of hashvalues compared favorably to facilitate traversing the hash treestructure to the lowest layer to identify the block(s) and/or listentries that correspond to a slice error.

FIG. 9 is a flowchart illustrating an example of identifying sliceerrors. The method begins at step 144 where a processing moduleretrieves root hash values from at least two pillars of a commondispersed storage (DS) unit storage set. Note that the processing modulemay determine which DS unit storage set based on one or more of a list,a predetermination, where comparison testing left off last time, anerror message, and a command. The processing module sends a retrieveroot hash value message to the DS units associated with the two or morepillars. For example, the processing module sends a retrieve root hashvalue message to all of n DS units (e.g., n=pillar width) associatedwith all pillars of the DS unit storage set. Next, the processing modulereceives n root hash values from the DS units.

The method continues at step 146 where the processing module determineswhether the root hash values compare favorably to each other. Forinstance, the same level root hash values compare favorably when theroot hash values are substantially the same (e.g., when there are nodifferences in the source name and revision lists). The method repeatsback to step 144 when the processing module determines that the roothash values compare favorably. The method continues to step 148 one theprocessing module determines that the root hash values unfavorably(e.g., one or more slice errors exist).

The method continues at step 148 where the processing module determinesa next layer down from the root hash values in accordance with a hashtree structure. The processing module determines the next layer downwhen a plurality of hash values are associated with the next layer down.Such a next layer down may be a first portion of a plurality of roothash values when the processing module initially retrieves root hashvalues from a next layer. Note that a portion may be a second or greaterportion of a plurality of root hash values when the processing module isretrieving root hash values from a next layer where the processingmodule has previously retrieved root hash values from a differentportion of a plurality of root hash values from a same layer.

The method continues at step 150 where the processing module determineswhether the hash values compare favorably to each other. The methodrepeats back to step 148 when the hash values compare favorably suchthat the processing module continues retrieving hash values fromdifferent portions of the same layer until all portions of the samelayer have been compared. Note that at least one portion of a layer ofroot hash values compares unfavorably when a previous comparison at ahigher layer indicated an unfavorable comparison. The method continuesto step 152 when the processing module determines that the hash valuescompare unfavorably.

At step 152 the processing module determines whether comparison testinghas exhausted all layers in accordance with the hash tree structure toisolate a portion of a list associated with a slice error. The methodrepeats back to step 148 when the processing module determines that allof layers have not been exhausted. The method continues to step 154 whenthe processing module determines that all of the layers have beenexhausted. At step 154 where the processing module retrieves source nameand revision list entries from two or more DS units corresponding to theblock(s) covered by a hash value comparison that was unfavorable. Themethod continues at step 156 where the processing module determinessource name errors based on comparing retrieved list entries. Note thaterrors are indicated when the list entries are not substantially thesame and that the processing module may retrieve a same entry fromsubstantially all pillars of the DS unit storage set to determineinformation of a majority and a minority of the list entries. Forexample, the processing module verifies a slice error in DS unit 3 whenall DS units returned a value that was identical except for an entryfrom DS unit 3.

FIGS. 10A-10B are schematic block diagrams of another embodiment of acomputing system where each includes a dispersed storage (DS) processingunit 158-160 and a DS unit storage set that includes DS units 1-4. In astorage example, DS unit 1 is utilized to store pillar 1 slices, DS unit2 stores pillar 2 slices, DS unit 3 stores pillar 3 slices, and DS unit4 stores pillar 4 slices.

FIG. 10A represents a scenario where DS unit 2 is not available to theDS processing unit 158 (e.g., DS unit 2 has failed, the network to DSunit 2 is not operational, and/or DS unit 2 is in a maintenance cycle).In such a scenario, the DS processing unit 158 utilizes the other threeDS units 1, 3, and 4 to store and retrieve slices in this DS unitstorage set. Successful operation may not be possible when one more ofthe other three DS units 1, 3, and 4 fails in a system where the pillarwidth is 4 and the decode threshold is 3.

In an example of operation, DS processing unit 158 detects that DS unit2 is unavailable, creates foster slices for pillar 2 (e.g., forsubsequent data segments to be stored in the DS unit storage set),determines an alternative DS unit as DS unit 1 to store the fosterslices, and send the foster slices to DS unit 1 to temporarily store thefoster slices while DS unit 2 remains unavailable. Note that fosterslices include slices that are normally stored in a second DS unitassociated with a second pillar such that the foster slices are at leasttemporarily stored in a first DS unit that is normally associated with afirst pillar where the first and second DS units are different and thefirst and second pillars a different. The DS processing unit 158retrieves the foster slices from the alternative DS unit (e.g., DS unit1) when the DS processing unit 158 determines to retrieve slicesnormally associated with the DS unit that is not available. Note thatthe DS processing unit 158 may send foster slices for storage to two ormore alternative DS units.

FIG. 10B represents a scenario where DS unit 2 transitions fromunavailable to available. The DS processing unit 160 facilitates movingfoster slices from the one or more alternative DS units (e.g., DS unit1) to the DS unit that has just transitioned from unavailable toavailable (e.g., to store the slices that DS unit 2 missed while it wasnot available). Alternatively, one or more of the alternative DS unitsthat contains foster slices determines that a DS unit that is associatedwith at least some of the foster slices has just transitioned fromunavailable to available. The one or more of the alternative DS unitsmay facilitate moving at least some of the foster slices from the one ormore of the alternative DS units to the DS unit that has justtransitioned from unavailable to available. Next, the DS processing unit160 retrieves the pillar 2 slices from DS unit 2 for the slices storedprevious to the available to unavailable transition of DS unit 2 and forthe slices stored while DS unit 2 was unavailable. The method to create,store, and retrieve foster slices is discussed in greater detail withreference to FIG. 11A-11B.

FIG. 11A is a flowchart illustrating an example of storing data, whichincludes similar steps to FIG. 6. The method begins with step 162 wherea processing module dispersed storage error encodes a data segment toproduce a set of encoded data slices. The method continues at step 112of FIG. 6 to determine DS units of the DS unit storage. The methodcontinues at step 166 where the processing module determines DS unitavailability based on one or more of a query, a list, a command, anerror message, and a message. Note that the DS unit availability may bea function of network availability to a site location associated withthe DS unit and/or operational health of the DS unit. The methodcontinues at step 168 where the processing module determines whether allDS units of the DS unit storage set are available. The method branchesto step 172 when the processing module determines that all of the DSunits are not available. The method continues to step 170 when theprocessing module determines that all of the DS units are available. Atstep 170, the processing module sends the set of encoded data slices tothe DS unit storage set for storage therein.

The method continues at step 172 where the processing module createsfoster encoded data slices for pillars corresponding to unavailable DSunits and the processing module creates non-foster encoded data slicescorresponding to the available units for remaining pillars. For example,the foster encoded data slices may be substantially the same as theencoded data slices created previously for those pillars that are notavailable. The method continues at step 174 where the processing moduledetermines alternative DS units to send the foster encoded data slicesto for storage based on one or more of a query, a list, a command, amessage, available DS units of the DS unit storage set, a proximity ofthe alternative DS unit to the unavailable DS unit, performance historyof the alternative DS unit, and reliability history of the alternativeDS unit. The method continues at step 176 where the processing modulesends the foster encoded data slices to the alternative DS units with astore command to at least temporarily store the foster encoded dataslices. The processing module sends the non-foster encoded data slicesto the other available DS units with a store command to store thenon-foster encoded data slices.

FIG. 11B is a flowchart illustrating an example of migrating data, whichincludes similar steps to FIGS. 6 and 11A. The method begins with step178 were a processing module determines if foster encoded data slicesare present based on one or more of a query, a list, a command, and amessage. For example, the processing module searches for foster slicesin a present dispersed storage (DS) unit associated with the processingmodule or in one or more other DS units by sending a query and receivinga query response from the other DS unit. The method repeats back to step178 when the processing module determines that foster slices are notpresent. The method continues to step 112 when the processing moduledetermines that foster slices are present.

The method continues at step 112 of FIG. 6 to determine DS units of theDS unit storage. The method continues with step 166 of FIG. 11A todetermine DS unit availability of the DS unit associated with the fosterslices. The method continues with step 184 where the processing moduledetermines whether to move foster encoded data slices based on the DSunit availability and/or a determination comparing present DS unitsstoring foster slices and different candidate DS units. In such ascenario, the processing module determines whether to move the fosterencoded data slices to a DS unit where they normally would be stored(e.g., the same pillar) or whether to move the foster encoded dataslices from a first temporary DS unit to a second temporary DS unitwhere the second temporary DS unit is a better choice. For example, theprocessing module determines to move the foster encoded data slices froma first temporary DS unit to a second temporary DS unit when the secondtemporary DS unit has a better reliability history than the firsttemporary DS unit.

As another example, the processing module determines to move the fosterencoded data slices from the first temporary DS unit to the DS unitnormally associated with the pillar of the foster encoded data slices(e.g., the normal DS unit for this pillar). The method repeats back tostep 178 when the processing module determines not to move fosterencoded data slices. The method continues to step 186 where theprocessing module determines to move foster encoded data slices. At step186, the processing module facilitates moving the foster encoded dataslices. Note that moving the foster encoded data slices may includesending a retrieval command to DS units storing the foster encoded dataslices, receiving the foster encoded data slices, determining a new DSunit to move the foster encoded data slices to, sending the fosterencoded data slices to the new DS unit with a store command to store thefoster encoded data slices, and sending a delete slice command to the DSunits that were storing the foster encoded data slices to delete thefoster encoded data slices.

FIGS. 12A-12B are schematic block diagrams of another embodiment of acomputing system that includes a dispersed storage (DS) processing unit188, 194, a DS unit storage set 190 that includes four DS units (e.g.,DS units 1-4 in FIG. 12A and DS units 2-5 in FIG. 12B), and at least oneother DS unit that is not included in the DS unit storage set 190, 196(e.g., DS unit 5 in FIG. 12A and DS unit 1 in FIG. 12B).

FIG. 12A represents the computing system where the DS processing unit188 sends slices for storage to DS units 1-4 of DS unit storage set 190.Note that DS unit 1 is utilized to store pillar 1 slices, DS unit 2stores pillar 2 slices, DS unit 3 stores pillar 3 slices, and DS unit 4stores pillar 4 slices. Note that DS unit 5 is not part of the DS unitstorage set 190. Note that DS units outside of the DS unit storage set190 may determine to provide storage resources to a DS processing unit188. Such a determination may be based on one or more of DS unit memorycapacity, DS unit memory utilization, DS unit availability, networkstatus relative to a DS unit, a request, a query, a command, a message,a predetermination, and a change in status indicator. For example, DSunit 5 determines to send a participation solicitation message 192 tothe DS processing unit 188 when DS unit 5 determines that DS unit 5 isavailable to store encoded data slices and that the DS unit 5 memoryutilization is substantially lower than a utilization threshold. Such aparticipation solicitation message 192 may include one or more of a DSunit identifier (ID), a DS unit memory capacity, a DS unit memoryutilization, a DS unit availability indicator, a network status relativeto the DS unit indicator, a request, DS unit reliability history, DSunit performance history, DS unit cost, DS unit geographic location, DSunit affiliation with other DSN systems, and a DS unit storage set ID.The DS processing unit 188 receives the participation solicitationmessage and processes the message as described with reference to FIG.12B.

FIG. 12B represents the computing system where DS processing unit 194considers a participation solicitation message 192 from DS unit 5. TheDS processing unit 194 determines whether to utilize DS unit 5 based onone or more of information in the solicitation message 192, a DS unitstorage set capacity, a DS unit storage set utilization, a DS unitstorage set performance indicator, a DS unit storage set reliabilityindicator, a command, a message, a predetermination, a list, and anerror message. For example, the DS processing unit 194 determines toutilize DS unit 5 to replace DS unit 1 when the DS processing unit 194determines that the DS unit 5 utilization and/or DS unit 5 reliabilityhistory is more favorable than similar metrics for DS unit 1. As anotherexample, DS processing unit 194 determines not to utilize DS unit 5 whenthe metrics associated with DS unit 5 are not substantially morefavorable than metrics associated with each of the DS units 1-4 of theDS unit storage set 190 under consideration.

The DS processing unit 194 sends a participation solicitation response198 to DS unit 5, wherein the response includes an assignment to DS unitstorage set 196 to store pillar 1 slices when the DS processing unit 194determines to utilize DS unit 5 in favor of DS unit 1. Next, the DSprocessing unit 194 facilitates moving pillar 1 slices from DS unit 1over to DS unit 5. The DS processing unit 194 updates a virtualdispersed storage network (DSN) address to physical location table toindicate that the pillar 1 slices are now stored at DS unit 5.

FIG. 13 is a flowchart illustrating an example of utilizing a dispersedstorage unit. The method begins with step 200 where a processing modulereceives a participation solicitation message from a new dispersedstorage (DS) unit. Such a participation solicitation message may includecontent as discussed previously with reference to FIG. 12A. The methodcontinues at step 202 where the processing module determines a candidateDS unit storage set based on one or more of information in theparticipation solicitation message, a list, a predetermination, acommand, and an error message. For example, the processing moduledetermines the DS unit storage set based on a requested DS unit storageset in the participation solicitation message. As another example, theprocessing module determines the DS unit storage set based on DS unitstorage set performance when the DS unit storage set performance isgreater than a performance threshold.

The method continues at step 204 where the processing module determinescandidate DS unit storage set performance metrics, wherein such metricsmay include one or more of reliability history, uptime history,performance history, cost information, access latency history, memorycapacity, and memory utilization. The method continues at step 206 wherethe processing module determines whether to utilize the new DS unitbased on one or more of information in the participation solicitationmessage, a list, a predetermination, a command, an error message, thecandidate DS unit storage sets, and the DS unit storage set performancemetrics. For example, the processing module determines to replace DSunit 1 of the DS unit storage set with DS unit 5 when DS unit 1 hasunfavorable reliability performance history. The method branches to step212 when the processing module determines to utilize the new DS unit.The method continues to step 208 when the processing module determinesnot utilize the new DS unit.

At step 208, the processing module determines whether there are other DSunit storage sets to consider. Such a determination may be based on oneor more of a list of DS unit storage sets, DS unit storage setperformance information, which DS unit storage sets have been consideredso far, a command, a message, an error message, and a list. The methodrepeats back to step 202 when the processing module determines toconsider other DS unit storage sets. The method continues to step 210when the processing module determines not to consider other DS unitstorage sets. At step 210, the processing module sends a participationsolicitation response that indicates a decline to the new DS unit whenthe processing module determines that there are no other DS unit storagesets to consider. Note that in such a scenario, there may be noadvantage to utilize the new DS unit.

The method continues at step 212 where the processing module updates avirtual dispersed storage network (DSN) address to physical locationtable based on the new DS unit identifier (ID). For example, theprocessing module replaces the reference to DS unit 1 with a referenceto DS unit 5 when the processing module has determined to utilize DSunit 5 in favor of DS unit 1 for a vault and DS unit storage set. Themethod continues at step 214 where the processing module facilitatesmoving encoded data slices from a previous DS unit to the new DS unit.For example, the processing module retrieves encoded data slices from DSunit 1, sends the encoded data slices to DS unit 5 with a store commandto store the encoded data slices, and sends a delete encoded data slicecommand to DS unit 1 when DS unit 5 indicates a confirmation that theencoded data slices have been successfully stored.

FIGS. 14A-14B are schematic block diagrams of another embodiment of acomputing system that includes a dispersed storage (DS) processing unit216-218 and DS units 1-6. In an example of operation, the DS processingunit 216-218 utilizes DS units 1-4 as a DS unit storage set when apillar width is 4. For instance, DS processing unit 216-218 utilizes DSunit 1 to store and/or retrieve pillar 1 encoded data slices, DS unit 2is utilized to store pillar 2 slices, DS unit 3 is utilized to storepillar 3 slices, and DS unit 4 is utilized to store pillar 4 slices.Note that DS units 5-6 may be utilized as auxiliary DS units totemporarily store encoded data slices on behalf of any DS unit 1-4 ofthe DS unit storage set as discussed below.

FIG. 14A represents a scenario where DS unit 2 determines to re-dispersepillar 2 encoded data slices to one or more other DS units. Such adetermination may be based on one or more of a detection of a DS unit 2failure, detection of a DS unit 2 shutdown, detection of a DS unit 2maintenance cycle, detection of a network failure, an error message, apower indicator, a weather indicator, an earthquake indicator, andestimated future availability indicator, a command, a message, a query,a flag, and a predetermination. Next, DS unit 2 determines which of thepillar 2 encoded data slices to re-disperse to at least one other DSunit from DS unit 2. Such a determination may be based on one or more ofa query response, a flag, a command, a message, a predetermination, acritical information indicator, a frequency of access indicator, anestimated time complete re-dispersal indicator, a priority indicator,and a performance indicator. Next, DS unit 2 determines re-dispersalparameters (e.g., error coding dispersal storage function parameters) toutilize in a re-dispersal process. The re-dispersal parameters mayinclude one or more of a slice format indicator, a pillar width, a writethreshold, a read threshold, a decode threshold, an encoding method, adecoding method, an encryption method, a decryption method, a key, andauxiliary DS unit choices. Such a determination of the re-dispersalparameters may be based on one or more of a candidate auxiliary DS unitlist, candidate auxiliary DS unit performance history information,candidate auxiliary DS unit reliability history information, a candidateauxiliary DS unit status indicator, a query response, a flag, a command,a message, a predetermination, a critical information indicator, afrequency of access indicator, an estimated time complete re-dispersalindicator, a priority indicator, and a performance indicator.

Next, DS unit 2 facilitates re-dispersal of pillar 2 encoded data slicesto the auxiliary DS units (e.g., DS units 5 and 6) from DS unit 2. In aninstance of replication, DS unit 2 replicates the pillar 2 encoded dataslices as-is (e.g., without further encoding) when the slice formatindicator indicates slices rather than sub-slices. In another instanceof replication, DS unit 2 further error encodes the pillar 2 encodeddata slices to produce sub-slices when the slice format indicatorindicates sub-slices rather than slices. In an example of operation whenthe slice format indicator indicates slices, DS unit 2 retrieves a firstportion of the pillar 2 encoded data slices from a memory of DS unit 2,sends the first portion of encoded data slices as re-dispersed pillar 2slices to DS unit 3 for storage therein, and receives a confirmationmessage from DS unit 3 that the encoded data slices have beensuccessfully stored in DS unit 3. Next, DS unit 2 sends a second portionof the pillar 2 encoded data slices as re-dispersed pillar 2 slices toDS unit 5 for storage therein. Next, DS unit 2 sends a third portion ofthe pillar 2 encoded data slices as re-dispersed pillar 2 slices to DSunit 6. Note that any portion (e.g., first, second, third) of slices maybe substantially the same as any other portion of slices when theperformance indicator indicates further reliability is desired.

In another example of operation when the slice format indicatorindicates sub-slices, DS unit 2 retrieves a slice of the pillar 2encoded data slices from the memory of DS unit 2, dispersed storageerror encodes the slice to produce sub-slices, sends the sub-slices toone or more other DS units (e.g., auxiliary DS units) for storagetherein, and receives a confirmation message from the other DS unitsthat the sub-slices have been successfully stored. Note that DS unit 2,an auxiliary DS unit 5-6, and/or the DS processing unit may maintain avirtual dispersed storage network (DSN) address to physical locationtable to enable the determination of a storage location of slices and/orsub-slices for a subsequent retrieval sequence. The method of operationto re-disperse slices is discussed in greater detail with reference toFIG. 15A.

FIG. 14B represents an example of operation where dispersed storage (DS)unit 2 determines whether pillar 2 encoded data slices are missing. Sucha determination may be based on one or more of a query, a flag, acommand, a message, a predetermination, a list, a comparison of a storedchecksum to a calculated checksum, a comparison of a stored integritytest value to a re-calculated integrity test value, and a comparison ofa portion of a DS unit 2 source name list to a source name list from adifferent DS unit of another pillar. Note that DS unit 2 may evaluatethis determination based on one or more of a power up sequence detectionindicator, a network restoration indicator, a maintenance cyclecompletion indicator, a repair complete indicator, a command, a message,a timer expiration since the last evaluation, and a predetermination.

DS unit 2 determines if slices were re-dispersed when DS unit 2determines that encoded data slices are missing based on one or more ofa flag, a command, a message, a predetermination, a list, a locallystored value, and a virtual DSN address to physical location tablelookup. Next, DS unit 2 determines how and where the slices werere-dispersed. Such a determination may be based on one or more ofretrieval of a slice format indicator, re-dispersal parameters,retrieval of dispersal parameters, operational parameters, an auxiliaryDS unit list, a query, a command, a message, and predetermination. DSunit 2 retrieves re-dispersed slices from other DS units correspondingto the missing slices. DS unit 2 stores the re-dispersed slices in amemory of DS unit 2. Note that DS unit 2 stores the retrievedre-dispersed slices as-is when a slice format indicator indicates slicesrather than sub-slices. DS unit 2 retrieves at least a decode thresholdnumber of sub-slices from auxiliary DS units, dispersed storage errordecodes the retrieved sub-slices to produce a re-created slice forstorage in the memory of DS unit 2 when the slice format indicatorindicates sub-slices rather than slices. DS unit 2 retrievesre-dispersed pillar 2 slices from DS unit 3 and stores the re-dispersedpillar 2 slices in the memory of DS unit 2. DS unit 2 retrievesre-dispersed pillar 2 slices from DS unit 5 and stores the re-dispersedpillar 2 slices in the memory of DS unit 2. DS unit 2 retrievesre-dispersed pillar 2 slices from DS unit 6 and stores the re-dispersedpillar 2 slices in the memory of DS unit 2. The method of operation toretrieve and store re-dispersed slices is discussed in greater detailwith reference to FIG. 15B.

FIG. 15A is a flowchart illustrating an example of re-dispersing anencoded data slice. The method begins with step 220 where a processingmodule detects a dispersed storage (DS) unit shutdown. Such a detectionmay be based on one or more of a detection of a DS unit failure,detection of a DS unit power down, detection of a DS unit maintenancecycle, detection of a network failure, an error message, a powerindicator, a weather indicator, an earthquake indicator, and estimatedfuture availability indicator, a command, a message, a query, a flag,and a predetermination.

The method continues with step 222 where the processing moduledetermines whether to re-disperse encoded data slices of the DS unit toone or more other DS units when the processing module detects theshutdown of the DS unit. Such a determination may be based on one ormore of a failure type, a detection of a DS unit failure, detection of aDS unit shutdown, detection of a DS unit maintenance cycle, detection ofa network failure, an error message, a power indicator, a weatherindicator, an earthquake indicator, and estimated future availabilityindicator, a command, a message, a query, a flag, and apredetermination. For example, the processing module determines tore-disperse encoded data slices when the processing module determinesthat a power fluctuation may last for a time period greater than a timethreshold as indicated by the power indicator. The method branches tostep 226 when the processing module determines to re-disperse encodeddata slices. The method ends at step 224 when the processing moduledetermines to not re-disperse encoded data slices.

The method continues at step 226 where the processing module determineswhich slices of the encoded data slices to re-disperse to at least oneother DS unit when the processing module determines to re-disperseencoded data slices. Such a determination may be based on one or more ofa query response, a flag, a command, a message, a predetermination, acritical information indicator, a frequency of access indicator, anestimated time to complete re-dispersal indicator, a priority indicator,and a performance indicator. For example, the processing moduledetermines to re-disperse a set of most critical slices as indicated bythe critical information indicator. As another example, the processingmodule determines to re-disperse as many slices as possible within atimeframe indicated by the estimated time to complete re-dispersalindicator (e.g., how much time left before the DS unit is completelydown and unable to transfer slices). As yet another example, theprocessing module determines to re-disperse encoded data slices that areaccessed most often as indicated by the frequency of access indicator.

The method continues at step 228 where the processing module determinesre-dispersal parameters (e.g., dispersed storage error codingparameters) to utilize in the re-dispersal process.

Such re-dispersal parameters may include one or more of a slice formatindicator (e.g., slices or sub-slices), a pillar width, a readthreshold, a read threshold, encoding method, decoding method, anencryption method, a decryption method, a key, and auxiliary DS unitchoices. Such a determination of the re-dispersal parameters may bebased on one or more of a candidate auxiliary DS unit list, candidateauxiliary DS unit performance history information, candidate auxiliaryDS unit reliability history information, a candidate auxiliary DS unitstatus indicator, a query response, a flag, a command, a message, apredetermination, a critical information indicator, a frequency ofaccess indicator, an estimated time to complete re-dispersal indicator,a priority indicator, and a performance indicator. For example, theprocessing module determines the re-dispersal parameters to include aslice format indicator that indicates slices are to be transferred asslices rather than as sub-slices when the processing module determinesthat time to complete the re-dispersal is relatively short which mayprevent creating sub-slices. As another example, the processing moduledetermines the re-dispersal parameters to include a particular auxiliaryDS unit, wherein the auxiliary DS unit has an above average performancehistory as indicated by the candidate auxiliary DS unit performancehistory information.

The method continues at step 230 where the processing module facilitatesre-dispersal of encoded data slices to the auxiliary DS units. Forexample, the processing module replicates the encoded data slices as-is(e.g., without further encoding) for storage in a different DS unit whenthe slice format indicator indicates slices rather than sub-slices. Asanother example, the processing module dispersed storage error encodesthe pillar 2 encoded data slices to produce sub-slices for storage in adifferent DS unit when the slice format indicator indicates sub-slicesrather than slices.

FIG. 15B is a flowchart illustrating another example of migrating data.The method begins with step 232 where a processing module determineswhether encoded data slices are missing based on one or more of a query,a flag, a command, a message, a predetermination, a list, a comparisonof a stored checksum to a calculated checksum, a comparison of a storedintegrity test value to a re-calculated integrity test value, and acomparison of a portion of a dispersed storage (DS) unit source namelist associated with a first pillar to a source name list from anotherDS unit associated with another pillar. Note that the processing modulemay initiate such a determination based on one or more of a power upsequence detection indicator, a network restoration indicator, amaintenance cycle completion indicator, a repair complete indicator, acommand, a message, a timer expiration since the last evaluation, and apredetermination. The method branches to step 236 when the processingmodule determines that encoded data slices are missing. The method endsat step 234 when the processing module determines that encoded dataslices are not missing.

The method continues at step 236 where the processing module determineswhether encoded data slices were re-dispersed when encoded data slicesare missing. Such a determination may be based on one or more of a flag,a command, a message, a predetermination, a list, a locally storedvalue, and a virtual dispersed storage network (DSN) address to physicallocation table lookup. The method branches to step 240 when theprocessing module determines that the encoded data slices were notre-dispersed. The method continues to step 238 when the processingmodule determines that the encoded data slices were re-dispersed.

The method continues at step 238 where the processing module determinesthe re-dispersal parameters (e.g., how and where the slices werere-dispersed). Such a determination may be based on one or more ofretrieval of a slice format indicator (e.g., slices or sub-slices),re-dispersal parameters, retrieval of dispersal parameters, operationalparameters, an auxiliary DS unit list, a query, a command, a message,and a predetermination. The method branches to step 242.

The method continues at step 240 where the processing module determinesdispersal parameters when the encoded data slices were not re-dispersed.The processing module determines the dispersal parameters (e.g., errorcoding dispersal storage function parameters) to utilize to dispersedstorage error encode encoded slices for storage as re-encoded dataslices for each pillar such that the re-encoded data slices from atleast a decode threshold number of pillars can be subsequently retrievedand dispersed storage error decoded to re-create at least one missingencoded data slice.

The method continues at step 242 where the processing module retrievesslices (e.g., slices from other pillars, re-dispersed slices fromauxiliary DS units, sub-slices from auxiliary DS units) from the DSunits corresponding to the missing slices. For example, the processingmodule provides re-dispersed slices as-is when the retrieved slices arere-dispersed slices. As another example, the processing module retrievesat least a decode threshold number of sub-slices from auxiliary DSunits, de-slices and decodes the sub-slices, and then re-encodes andre-slices to produce slices of the missing slices when the slices aresub-slice. As yet another example, the processing module retrieves atleast a decode threshold number of slices from DS units of otherpillars, de-slices and decodes the slices from other pillars, and thenre-encodes and re-slices to produce slices of the missing slices whenthe slices are slices stored on other pillars.

The method continues at step 244 where the processing module facilitatesstorage of the slices in a DS unit that has the missing slices. Notethat the processing module stores the retrieved re-dispersed slicesas-is when the slice format indicator indicates slices rather thansub-slices or slices from other pillars. In addition, the processingmodule may send a delete command to the auxiliary DS units and/or the DSunits of other pillars to delete the recently retrieve slices once themissing slices have been re-created and stored on the DS unit.

FIG. 16A is a flowchart illustrating an example of replicating anencoded data slice. The method begins with step 246 where a processingmodule detects an off-line dispersed storage (DS) unit. Such a detectionmay be based on one or more of a detection of a DS unit failure,detection of a DS unit shutdown, detection of a DS unit maintenancecycle, detection of a network failure, an error message, a powerindicator, a weather indicator, an earthquake indicator, and estimatedfuture availability indicator, a command, a message, a query, a flag,and a predetermination.

The method continues at step 248 where the processing module determineswhether to replicate encoded data slices to one or more other DS units.Such a determination may be based on one or more of a failure type, adetection of a DS unit failure, detection of a DS unit shutdown,detection of a DS unit maintenance cycle, detection of a networkfailure, an error message, a power indicator, a weather indicator, anearthquake indicator, and estimated future availability indicator, acommand, a message, a query, a flag, and a predetermination. Forexample, the processing module determines to replicate encoded dataslices when a power outage may last for five hours as signaled by thepower indicator. The method branches to step 252 when the processingmodule determines to replicate. The method continues to step 250 whenthe processing module determines not to replicate. The method ends atstep 250.

The method continues at step 252 where the processing module determineswhich of the encoded data slices to replicate by sending encoded dataslices to at least one other DS unit. Such a determination may be basedon one or more of a query response, a flag, a command, a message, apredetermination, a critical information indicator, a frequency ofaccess indicator, an estimated time to complete replication indicator, apriority indicator, and a performance indicator. For example, theprocessing module determines to replicate the most critical slices asdetermined by the critical information indicator. As another example,the processing module determines to replicate slices that are accessedmost often as indicated by the frequency of access indicator.

The method continues at step 254 where the processing module determinesreplication parameters (e.g., dispersed storage error coding parameters)to utilize in the replication process. Such replication parameters mayinclude one or more of a pillar width, a write threshold, a readthreshold, a decode threshold, encoding method, decoding method, anencryption method, a decryption method, a key, other DS units of theother pillars of the storage set of the DS unit, and auxiliary DS unitchoices. Such a determination of the replication parameters may be basedon one or more of a candidate auxiliary DS unit list, candidateauxiliary DS unit performance history information, candidate auxiliaryDS unit reliability history information, a candidate auxiliary DS unitstatus indicator, a query response, a flag, a command, a message, apredetermination, a critical information indicator, a frequency ofaccess indicator, an estimated time to complete replication indicator, apriority indicator, and a performance indicator. For example, theprocessing module determines the replication parameters to include aparticular auxiliary DS unit where the auxiliary DS unit has an aboveaverage performance history as indicated by the candidate auxiliary DSunit performance history information.

The method continues at step 256 where the processing module facilitatesreplication of encoded data slices to the auxiliary DS units. Forexample, the processing module retrieves encoded data slices of otherpillars from other DS units of a DS unit storage set, de-slices anddecodes the slices to produce a data segment, re-encodes and re-slicesthe data segment to produce replicated slices of the slices to bereplicated. Next, the processing module sends the replicated slices tothe auxiliary DS units with a store command to store the replicatedslices. Note that the processing module may update a virtual dispersedstorage network (DSN) address to physical location table to enablesubsequent retrieval of the replicated slices when the DS unit is backonline.

FIG. 16B is a flowchart illustrating another example of migrating data,which includes similar steps to FIG. 15B. The method begins with step232 of FIG. 15B where a processing module determines whether slices aremissing. The method branches to step 262 when the processing moduledetermines that slices are missing. The method ends at step 260 when theprocessing module determines that slices are not missing. The methodcontinues at step 262 where the processing module determines whetherslices were replicated. Such a determination may be based on one or moreof a flag, a command, a message, a predetermination, a list, a locallystored value, and a virtual DSN address to physical location tablelookup. The method branches to step 266 when the processing moduledetermines that the slices were not replicated. The method continues tostep 264 when the processing module determines that the slices werereplicated.

The method continues at step 264 where the processing module determinesreplication parameters (e.g., how and where the slices were replicated)when the processing module determines that slices were replicated. Sucha determination may be based on one or more of retrieval of replicationparameters, operational parameters, an auxiliary DS unit list, a query,a command, a message, and a predetermination. The method branches tostep 242.

The method continues at step 266 where the processing module determinesoperational parameters (e.g., dispersed storage error coding parameters)when the processing module determines that slices were not replicated.The processing module determines the operational parameters to includeparameters recently utilized to create the slices. The method continueswith step 242 FIG. 15B where the processing module retrieves andprocesses the slices and then continues with step 244 of FIG. 15B tofacilitate storage of the slices.

FIG. 17 is a schematic block diagram of another embodiment of acomputing system that includes a user device domain 272, a dispersedstorage (DS) processing unit 16, and a dispersed storage network (DSN)memory 22. The user device domain 272 includes user devices 1-3. Notethat the user device domain 272 may include any number of user devices.The DS processing unit 16 includes a DS processing 34 and the DSN memory22 includes a plurality of DS units 1-N. Such user devices 1-3 of theuser device domain 272 are associated with a common user such that data,information, and/or messages traversed by the user devices 1-3 sharerelationship with the common user. The DS processing unit 16 providesuser device 1 access to the DSN memory 22 when the user device 1 doesnot include a DS processing 34.

The user devices 1-3 may include fixed or portable devices as discussedpreviously (e.g., a smart phone, a wired phone, a laptop computer, atablet computer, a desktop computer, a cable set-top box, a smartappliance, a home security system, a home automation system, etc.). Theuser devices 1-3 may include a computing core, one or more interfaces,the DS processing 34 and/or a collection module 274. For example, userdevice 1 includes the collection module 274. User device 2 includes thecollection module 274 and the DS processing 34. User device 3 includesthe DS processing 34 which includes the collection module 274. Thecollection module 274 includes a functional entity (e.g., a softwareapplication that runs on a computing core or as part of a processingmodule) that intercepts user data, processes the user data to produce adata representation, and/or facilitates storage of the datarepresentation in the DSN memory in accordance with one or more ofmetadata, preferences, and/or operational parameters (e.g., dispersedstorage error coding parameters).

In an example operation, the user devices 1-3 traverse the user datafrom time to time where the user data may include one or more of bankinginformation, home video, video broadcasts, pictures from a user camera,e-mail messages, short message service messages, class notes, websitevisits, web downloads, contact lists, social networking connections,school grades, medical records, social networking messaging, passwordlists, and any other user data type associated with the user. Note thatthe user data may be communicated from one user device to another userdevice and/or from a user device to a module or unit external to thecomputing system. Further note that the user data may be stored in anyone or more of the user devices 1-3.

In another example of operation, the collection module 274 of userdevice 1 intercepts medical records that are being processed by userdevice 1. The collection module 274 determines metadata based on themedical records and determines preferences based on a user identifier(ID). The collection module 274 determines whether to archive themedical records based in part on the medical records, the metadata, andthe preferences. The collection module 274 processes the medical recordsin accordance with the preferences to produce a data representation whenthe collection module 274 determines to archive the medical records. Forexample, the collection module 274 of the user device 1 sends the datarepresentation 275 to the DS processing unit 16. The data representation275 may include one or more of the data, the metadata, the preferences,and storage guidance. The DS processing unit 16 determines operationalparameters, creates encoded data slices based on the datarepresentation, and sends the encoded data slices 11 to the DSN memory22 with a store command to store the encoded data slices 11. As anotherexample, the collection module 274 of the user device 1 determinesoperational parameters based in part on one or more of the user data,the metadata, the preferences, and the data representation. Next, thecollection module 274 sends the data representation 275 to the DSprocessing unit 16. In this example, the data representation 275 mayinclude one or more of the operational parameters, the metadata, thepreferences, and storage guidance. The DS processing unit 16 determinesfinal operational parameters based in part on the operational parametersfrom the collection module 274, creates encoded data slices based on thedata representation and the final operational parameters, and sends theencoded data slices 11 to the DSN memory 22 with a store command tostore the encoded data slices 11.

In yet another example of operation, the collection module 274 of userdevice 2 intercepts banking records that are being viewed by user device2. The collection module 274 determines metadata based on the bankingrecords and determines preferences based on a user ID. The collectionmodule 274 determines whether to archive the banking records based onthe banking records, the metadata, and the preferences. The collectionmodule 274 processes the banking records in accordance with thepreferences to produce a data representation when the collection moduledetermines to archive the banking records. For example, the collectionmodule 274 sends the data representation to the DS processing 34 of DSunit 2 such that the data representation may include one or more of themetadata, the preferences, and storage guidance. The DS processing 34determines operational parameters, creates encoded data slices based onthe data representation, and sends the encoded data slices 11 to the DSNmemory 22 with a store command to store the encoded data slices 11. Asanother example, the collection module 274 determines operationalparameters based on one or more of the user data (e.g., the bankingrecords), the metadata, the preferences, and the data representation.The collection module 274 sends the data representation to the DSprocessing 34 of DS unit 2, wherein the data representation includes oneor more of the operational parameters, the metadata, the preferences,and storage guidance. The DS processing 34 determines final operationalparameters based in part on the operational parameters from thecollection module, creates encoded data slices based on the datarepresentation and the final operational parameters, and sends theencoded data slices 11 to the DSN memory 22 with a store command tostore the encoded data slices 11.

In a further example of operation, the collection module 274 of userdevice 3 intercepts home video files that are being processed by userdevice 3. The collection module 274 determines metadata based on one ormore of the home video files and determines preferences based in part ona user ID. The collection module 274 determines whether to archive thehome video files based on the home video files, the metadata, and thepreferences. The collection module 274 processes the home video files inaccordance with the preferences to produce a data representation whenthe collection module 274 determines to archive the home video files.For example, the collection module 274 sends the data representation tothe DS processing 34 of DS unit 3, wherein the data representationincludes one or more of the metadata, the preferences, and storageguidance. The DS processing 34 determines operational parameters,creates encoded data slices based on the data representation and theoperational parameters, and sends the encoded data slices 11 to the DSNmemory 22 with a store command to store the encoded data slices 11. Asanother example, the collection module 274 determines operationalparameters based on one or more of the user data (e.g., the home videofiles), the metadata, the preferences, and the data representation. Thecollection module 274 sends the data representation to the DS processing34 of DS unit 3, wherein the data representation includes one or more ofthe operational parameters, the metadata, the preferences, and storageguidance. The DS processing 34 determines final operational parametersbased on the operational parameters from the collection module 274,creates encoded data slices based on the data representation and thefinal operational parameters, and sends the encoded data slices 11 tothe DSN memory 22 with a store command to store the encoded data slices11.

FIG. 18 is a flowchart illustrating an example of archiving data. Themethod begins with step 276 where he processing module captures userdata. Such capturing may include one or more of monitoring a data streambetween a user device and an external entity, monitoring a data streaminternally between functional elements within the user device, andretrieving stored data from a memory of the user device. The methodcontinues at step 278 where the processing module determines metadata,wherein the metadata may include one or more of a user identifier (ID),a data type, a source indicator, a destination indicator, a contextindicator, a priority indicator, a status indicator, a time indicator,and a date indicator. Such a determination may be based on one or moreof the captured user data, current activity or activities of the userdevice (e.g., active processes, machines state, input/outpututilization, memory utilization, etc.), geographic location information,clock information, a sensor input, a user record, a lookup, a command, apredetermination, and message. For example, the processing moduledetermines the metadata to include a banking record data type indicatorand a geographic location-based context indicator when the processingmodule determines the banking data type and geographic locationinformation.

The method continues with step 280 where the processing moduledetermines preferences, wherein the preferences may include one or moreof archiving priority by data type, archiving frequency, contextpriority, status priority, volume priority, performance requirements,and reliability requirements. Such a determination may be based on oneor more of the user ID, the user data, the metadata, contextinformation, a lookup, a predetermination, a command, a query response,and a message. The method continues at step 282 where the processingmodule determines whether to archive data based on one or more of themetadata, context information, a user ID, a lookup, the preferences, anda comparison of the metadata to one or more thresholds. For example, theprocessing module determines to archive data when the metadata indicatesthat the user data comprises new banking records. As another example,the processing module determines to not archive data when the metadataindicates that the user data comprises routine website accessinformation. The method repeats back to step 276 when the processingmodule determines not to archive data. The method continues to step 284when the processing module determines to archive data.

The method continues at step 284 where the processing module processesthe user data to produce a data representation, wherein the datarepresentation may be in a compressed and/or a transformed form tofacilitate storage in a dispersed storage network (DSN) memory. Theprocessing module processes the data based on one or more of thecaptured data, the metadata, the preferences, a processing method tablelookup, a command, a message, and a predetermination. For example, theprocessing module processes the user data to produce a datarepresentation where a size of the data representation facilitates anoptimization of DSN memory storage efficiency. For instance, the datarepresentation size may be determined to align with a data segment anddata slice sizes such that memory is not unnecessarily underutilized asdata blocks are stored in dispersed storage (DS) units of the DSNmemory.

The method continues at step 286 where the processing module determinesoperational parameters. Such a determination may be based on one or moreof the data representation, the captured user data, the metadata, thepreferences, a processing method table lookup, a command, a message, anda predetermination. For example, the processing module determines apillar width and decode threshold such that an above average reliabilityapproach to storing the data representation is provided when theprocessing module determines that the metadata indicates that the userdata comprises very high priority financial records requiring a verylong term of storage without failure.

The method continues at step 288 where the processing module facilitatesstorage of the data representation in the DSN memory. For example, theprocessing module creates dispersed storage error encodes the datarepresentation utilizing the operational parameters to produce encodeddata slices. Next, the processing module sends the encoded data slicesto the DS units of the DSN memory for storage therein.

FIG. 19 is a flowchart illustrating another example of storing data,which includes similar steps to FIG. 6. The method begins with steps 102and 104 of FIG. 6 where a processing module receives a store data objectmessage and determines dispersed storage error coding parameters. Themethod continues at step 292 where the processing module encodes data toproduce a plurality of sets of encoded data slices in accordance withthe dispersed storage error coding parameters.

The method continues at step 294 where, for a set of encoded data slicesof a plurality of sets of encoded data slices, the processing moduledetermines whether one or more of the encoded data slices of the set ofencoded data slices are required encoded data slices to produce one ormore required encoded data slices. Such a determination may include oneor more of determining a security protocol for the plurality of sets ofencoded data slices, wherein the security protocol indicates a use ofrequired encoded data slices and determining a performance protocol forthe plurality of sets of encoded data slices, wherein the performanceprotocol indicates the use of required encoded data slices. Note thatthe indication of use includes at least one of identifying one or morespecific encoded data slices as the one or more required encoded dataslices and determining the one or more required data slices based on oneor more of selecting one or more dispersed storage error codingparameters, analyzing a dispersed storage (DS) unit operationalinformation, performing a vault lookup, interpreting a storage requestmessage, and interpreting a command.

As an example of step 294, the processing module determines that encodeddata slices 1-10 of a set of encoded data slices 1-16 are requiredencoded data slices when the performance protocol for the plurality ofsets of encoded data slices includes an indication of dispersed storageerror coding parameters including a pillar width of 16 and a decodethreshold of 10. As another example, the processing module determinesthat encoded data slices 5-8 of the set of encoded data slices 1-6 arerequired encoded data slices when the security protocol includes anindication that corresponding DS units operational information include ahigh-security indicator. The method branches to step 298 when theprocessing module determines that none of the encoded data slices arerequired encoded data slices. The method continues to step 296 when theprocessing module determines that at least one of the encoded dataslices is a required encoded data slice.

At step 296 the processing module generates specific dispersed storagenetwork (DSN) storage information for each of the one or more requiredencoded data slices. The specific DSN storage information includes for afirst one of the one or more required encoded data slices, a first DSunit identification code, a first slice name, and a first instruction tostore the first one of the one or more required encoded data slicesbased on the first slice name at a first DS unit that corresponds to thefirst DS unit identification code and for a second one of the one ormore required encoded data slices, a second DS unit identification code,a second slice name, and a second instruction to store the second one ofthe one or more required encoded data slices based on the second slicename at a second DS unit that corresponds to the second DS unitidentification code. For example, the processing module generatesspecific DSN storage information for required encoded data slices thatincludes for the first one of the one or more required encoded dataslices a first DS unit identification code of 1, a first slice name of457, and a first instruction to store the first one of the one or morerequired encoded data slices in a mandatory fashion and for the secondone of the one or more required encoded data slices a second DS unitidentification code of 2, a second slice name of 458, and a secondinstruction to store the second one of the one or more required encodeddata slices in a priority fashion.

The method continues at step 298 where the processing module generatesgeneral DSN storage information for remaining encoded data slices of theset of encoded data slices. The general DSN storage information includesidentification codes for a set of DS units and an instruction to storethe remaining encoded data slices in the set of DS units. For example,the processing module generates general DSN storage information for theremaining encoded data slices of the set of encoded data slices toinclude identification codes 11-16 for DS units 11-16 and an instructionto store the remaining encoded data slices in DS units 11-16 utilizing abest effort storage approach.

The method continues at step 304 where the processing module sends theset of encoded data slices to a DSN memory in accordance with thespecific DSN storage information and the general DSN storageinformation. In addition, the processing module may append additionaldata (e.g., a data storage priority, a data storage approach, a datatype indicator, the specific DSN storage information, the general DSNstorage information) to at least one of the one or more required encodeddata slices prior to sending a set of encoded data slices. For example,the processing module sends required encoded data slice 1 to DS unit 1,required encoded data slice 2 to DS unit 2, required encoded data slice3 to DS unit 3, through required encoded data slice 10 to DS unit 10, inaccordance with the specific DSN storage information and encoded dataslices 11-16 to any DS unit of DS units 16, 20, 33, 38, 51, and 60 inaccordance with the general DSN storage information when a pillar widthis 16 and a decode threshold is 10.

The method continues at step 306 where the processing module determineswhether a favorable storage response message was received within astorage time period for the one or more required encoded data slices.Note that an unfavorable storage response message may include anindication of one or more of a transaction conflict, a slice nameassociated with the required encoded data slices locked, and addressingerror, an expected slice revision is not present, and an unauthorizedrequest. Further note that a favorable storage response message mayinclude an indication of no error and/or operation succeeded. The methodbranches to step 310 when the processing module determines that thefavorable storage response message was received within the storage timeperiod. The method continues to step 308 where the method ends when theprocessing module determines that the favorable storage response messagewas received within the storage time period.

The method continues at step 310 where the processing module determinesalternate specific DSN storage information for at least one of the oneor more required encoded data slices. For example, the processing moduledetermines the alternate specific DSN storage information to includesending required encoded data slice 10 to DS unit 20 when a favorablestorage response message was not received from DS unit 10 within thestorage time period. As another example, the processing moduledetermines the alternate specific DSN storage information to includechanging required encoded data slice 10 to be not required encoded dataslice 10 and changing not required encoded data slice 11 to be requiredencoded data slice 11 to be stored at DS unit 10. The method continuesat step 312 where the processing module sends the at least one of theone or more required encoded data slices to the dispersed storagenetwork in accordance with the alternate specific DSN storageinformation. For example, the processing module sends encoded data slice10 to DS unit 20. As another example, the processing module sendsencoded data slice 11 to DS unit 10.

FIG. 20 is a flowchart illustrating an example of retrieving data, whichincludes similar steps to FIGS. 7 and 19. The method begins with step116 of FIG. 7 where a processing module receives a retrieve data objectmessage and continues with step 314 where the processing module requestsretrieval of encoded data slices associated with the retrieve dataobject message. The method continues at step 316 where the processingmodule receives at least some encoded data slices of a set of encodeddata slices of a plurality of sets of encoded data slices. The methodcontinues at step 294 of FIG. 19 where the processing module determineswhether any encoded data slices are required encoded data slices. Themethod branches to step 134 of FIG. 7 when the processing moduledetermines that none of the encoded data slices are required encodeddata slices. The method continues to step 318 when the processing moduledetermines that at least one encoded data slice is a required encodeddata slice.

At step 318 the processing module determines whether the one or morerequired encoded data slices was received in accordance with specificdispersed storage network (DSN) retrieval information. For example, theprocessing module determines that the one or more required encoded dataslices were received in accordance with the specific DSN retrievalinformation when each of the required encoded data slices was receivedfrom an expected corresponding DS unit of the specific DSN retrievalinformation. The method branches to step 134 of FIG. 7 when theprocessing module determines that the required encoded data slices werereceived in accordance with the specific DSN storage information. Themethod continues to step 319 when the processing module determines thatthe required encoded data slices were not received in accordance withthe specific DSN storage information.

At step 319, the processing module determines whether there is anotherapproach to receiving required encoded data slices is available. If not,an error is generated. If yes, the method continues at step 320 wherethe processing module determines a subsequent data retrieval approachbased on the specific DSN retrieval information. Such determiningincludes one or more of determining to re-request retrieval of the atleast one of the one or more required encoded data slices, determiningwhether the specific DSN retrieval information includes alternatespecific DSN retrieval information, and determining whether a lowerquality data retrieval method is allowed. For example, the processingmodule determines the subsequent data retrieval approach to includere-requesting retrieval of the least one of the one or more requiredencoded data slices when the specific DSN retrieval information requiresspecific slices to be retrieved from specific DS units. As anotherexample, the processing module determines the subsequent data retrievalapproach to include requesting retrieval of an alternate encoded dataslice as a required encoded data slice from an alternate DS unit whenthe processing module determines that the specific DSN retrievalinformation includes alternate specific DSN retrieval informationincluding a slice name of the alternate encoded data slice and anidentifier code of the alternate DS unit.

The method continues at step 322 where the processing module requestsretrieval of the at least one of the one or more required encoded dataslices in accordance with the subsequent data retrieval approach. Forexample, the processing module requests re-retrieval of the requiredencoded data slice when the subsequent data retrieval approach includesre-requesting retrieval of the required encoded data slice. As anotherexample, the processing module requests retrieval of the alternateencoded data slice when the subsequent data retrieval approach includesrequesting an alternate encoded data slice as the required encoded dataslice. The method continues at step 324 where the processing modulereceives the required encoded data slice. The method continues at step134 of FIG. 7 where the processing module dispersed storage errordecodes encoded data slices to reproduce the data object.

FIG. 21 is a flowchart illustrating another example of retrieving data,which includes similar steps to FIGS. 6 and 7. The method begins withstep 116 of FIG. 7 where a processing module receives a retrieve dataobject message from a requester. The method continues with step 348where the processing module determines access control information,wherein such access control information may indicate one or more ofaccess control by data object, access control by data segment, accesscontrol by data segment and by slice name, access by user identifier(ID), access by group ID, maximum number of allowed access sequences,and cumulative number of access sequences. Such a determination may bebased on one or more of information received in the retrieve data objectmessage, a user ID, a group ID, a data object name, a segment ID, asegment count, the slice name, a data type, a vault lookup, an accesscontrol list lookup, an access control list query, a command, a message,and a predetermination. For example, the processing module determinesthat the access control information indicates that access to the dataobject is controlled on a data segment by data segment basis whereaccess is controlled for each data segment of the data object. Note thatdata segments of the same data object may be stored in two or more DSunit storage sets when the access control is data segment by datasegment.

The method continues at step 350 where the processing module determineswhether access control is data segment by data segment based on theaccess control information. The method branches to step 364 when theprocessing module determines that access control is data segment by datasegment. The method continues to step 352 when the processing moduledetermines that access control is not data segment by data segment(e.g., access control may be by data object). At step 352 the processingmodule determines whether the data object request is authorized based onone or more of information in the retrieve data object message, theaccess control information, an access control list lookup, an accesscontrol list query, an access control list update, a vault lookup, acommand, a message, and predetermination. For example, the processingmodule determines that the data object request is authorized when a userID associated with the request matches a user ID on an access controllist that is allowed to access the requested data object. The methodbranches to step 112 of FIG. 6 when the processing module determinesthat the data object request is authorized. The method ends with step354 where the processing module sends a retrieve data object rejectmessage to the requester when the processing module determines that thedata object request is not authorized.

At step 112 the processing module determines dispersed storage (DS)units of a DS unit storage set. The method continues at step 358 wherethe processing module retrieves encoded data slices corresponding to thedata object from the DS units of the DS unit storage set. The methodcontinues at step 342 where the processing module dispersed storageerror decodes at least a decode threshold number of encoded data slicesper set of a plurality of sets of encoded data slices corresponding tothe data object to produce a plurality of data segments, aggregating theplurality of data segments to re-create the data object. The methodcontinues at step 344 where the processing module sends the data objectto the requester.

At step 364 the processing module determines a data segment when theprocessing module determines that access control is data segment by datasegment. For example, the processing module starts with a first datasegment of the data object. The method continues at step 366 for theprocessing module determines whether access of the data segment isauthorized based on a comparison of a data segment ID to an accesscontrol list comprising at least a list of authorized data segment IDsassociated with the requester (e.g., by user ID and/or by group ID). Themethod branches to step 370 when the processing module determines thataccess to the data segment is authorized. The method continues to step354 when the processing module determines that access to the datasegment is not authorized. The method ends with step 354 where theprocessing module sends the retrieve data object reject message to therequester.

At step 370 the processing module determines DS units that correspond towhere encoded data slices are stored for the data segment based on oneor more of a data object name to source name/slice name conversion(e.g., a translation of the data object name to a virtual dispersedstorage network (DSN) address), a virtual DSN address to physicallocation table lookup, a command, a message, and predetermination. Notethat two or more of the data segments of the data object may be storedin different DS unit storage sets. The processing module may determinedispersed storage error coding parameters based on one or more of theuser ID, a data object ID, a data segment ID, the present data segmentID, a slice name, information received in the retrieve data objectmessage, an individual user vault lookup, a group vault lookup, a list,a table, a command, a message, and a predetermination. Note that two ormore of the data segments of the data object may utilize differentdispersed storage error coding parameters.

The method continues at step 372 where the processing module retrievesencoded data slices from at least a decode threshold number of DS unitsof the DS unit storage set associated with the data segment by sendingretrieve encoded data slice commands to the DS units and receivingencoded data slices in response. The method continues at step 374 wherethe processing module dispersed storage error decodes at least a decodethreshold number of encoded data slices to re-create the data segment.The method continues at step 376 where the processing module determineswhether a last segment a plurality of data segments of the data objecthas been recreated (e.g., all of the segments) based on comparing anumber of re-created data segments to a number of data segmentsassociated with the data object. The method repeats back steps 364 whenthe processing module determines that the last data segment has not beenre-created. The method continues to step 378 when the processing moduledetermines that the last segment has been re-created. At step 378 theprocessing module aggregates the re-created data segments to re-createthe data object. The method continues at step 344 where the processingmodule sends the data object to the requester.

FIG. 22 is a diagram illustrating an example of encoded data sliceaccess sequences that includes a representation of an access sequence ofpillars 2, 3, 1, and 4, a representation of an access sequence ofsegments 4, 1, 5, 3, 6, and 2, and a representation of an orderedplurality of sets of encoded data slices 380. Such access sequences maybe utilized to provide the ordered plurality of sets of encoded dataslices 380. Note that a set of encoded data slices may include encodeddata slices of a data segment of a plurality of data segments of a datafile and encoded data slices of the plurality of data segments having acommon pillar number.

The access sequence of pillars 2, 3, 1, and 4 implies that encodedslices of pillar 2 are accessed first, encoded data slices of pillar 3are accessed second, encoded data slices of pillar 1 are accessed third,and encoded data slices of pillar 4 are accessed fourth. Sequencing ofencoded data slices of a common pillar includes one of an orderedsequence, a random sequence, and a pseudorandom sequence. For example,any encoded data slice of encoded data slices of pillar 3 may beaccessed in any order when the sequencing of the encoded data slices ofpillar 3 includes a random sequence. As another example, encoded dataslices of pillar 3 may be accessed in an order of slice 1_3, slice 2_3,slice 3_3, slice 4_3, slice 5_3, and slice 6_3 when the sequencing ofencoded data slices of pillar 3 includes an ordered sequence of slice1_3, slice 2_3, slice 3_3, slice 4_3, slice 5_3, and slice 6_3. Thesequencing of slices when utilizing the access sequence of pillars 2, 3,1, and 4 produces sets of encoded data slices by pillars 381. The setsof encoded data slices by pillars 381 are utilized to produce theplurality of sets of encoded data slices 380 such that encoded dataslices are organized both by segment and by pillar. For example, slices1-6 of pillar 2 are accessed first to fill in a second column of theplurality of sets of encoded data slices 380, slices 1-6 of pillar 3 areaccessed second to fill in a third column of the plurality of sets ofencoded data slices 380, slices 1-6 of pillar 1 are accessed third tofill in a first column of the plurality of sets of encoded data slices380, and slices 1-6 of pillar 4 are accessed fourth to fill in a fourthcolumn of the plurality of sets of encoded data slices 380.

The access sequence of segments 4, 1, 5, 3, 6, and 2 implies thatencoded slices of segment 4 are accessed first, encoded data slices ofsegment 1 are accessed second, encoded data slices of segment 5 areaccessed third, encoded data slices of segment 3 are accessed fourth,encoded data slices of segment 6 are accessed fifth, and encoded dataslices of segment 2 are accessed sixth. Sequencing of encoded dataslices of a common segment includes one of an ordered sequence, a randomsequence, and a pseudorandom sequence. For example, any encoded dataslice of encoded data slices of segment 4 may be accessed in any orderwhen the sequencing of the encoded data slices of segment 4 includes arandom sequence. As another example, encoded data slices of segment 4may be accessed in an order of slice 4_1, slice 4_2, slice 4_3, andslice 4_4 when the sequencing of encoded data slices of segment 4includes an ordered sequence of slice 4_1, slice 4_2, slice 4_3, andslice 4_4. The sequencing of slices when utilizing the access sequenceof segments 4, 1, 5, 3, 6, and 2 produces sets of encoded data slices bysegments 383. The sets of encoded data slices by segments 383 areutilized to produce the plurality of sets of encoded data slices 380such that encoded data slices are organized both by segment and bypillar. For example, slices 1-4 of segment 4 are accessed first to fillin a fourth row of the plurality of sets of encoded data slices 380,slices 1-4 of segment 1 are accessed second to fill in a first row ofthe plurality of sets of encoded data slices 380, slices 1-4 of segment5 are accessed third to fill in a fifth row of the plurality of sets ofencoded data slices 380, slices 1-4 of segment 3 are accessed fourth tofill in a third row of the plurality of sets of encoded data slices 380,slices 1-4 of segment 6 are accessed fifth to fill in a sixth row of theplurality of sets of encoded data slices 380, and slices 1-4 of segment2 are accessed sixth to fill in a second row of the plurality of sets ofencoded data slices 380.

FIG. 23 is a flowchart illustrating another example of retrieving data.The method begins with step 382 where a processing module receives adata retrieval request to retrieve data stored as a plurality of sets ofencoded data slices in a dispersed storage network (DSN) memory, whereinthe data retrieval request includes a data identifier (ID). Note thatthe set of encoded data slices includes at least one of encoded dataslices of a data segment of a plurality of data segments of a data fileand encoded data slices of the plurality of data segments having acommon pillar number.

The method continues at step 384 where the processing module determinesan access sequence for retrieving the plurality of sets of encoded dataslices based on the data ID. Such an access sequence includes at leastone of a series of ordered slice names of the plurality of sets of slicenames, a series of ordered segment identification codes, and a series ofordered pillar identification codes. Such a determination may be basedon at least one of the data ID, a requester ID, a source name, a datatype indicator, a vault lookup, a predetermination, a command, amessage, a dispersed storage (DS) processing unit ID, a priorityindicator, a performance indicator, and a reliability indicator. Forexample, the processing module determines the access sequence based on avault lookup utilizing the requester ID as an index for the vaultlookup. As another example, the processing module determines the accesssequence based on a vault lookup utilizing the data ID as an index forthe vault lookup. As yet another example, the processing moduledetermines access sequence based on a vault lookup utilizing the data IDand the requester ID as indexes for the vault lookup.

The method continues at step 386 where the processing module sends aslice retrieval message for a set of encoded data slices of theplurality of sets of encoded data slices. The method continues with step388 where the processing module receives at least a decode thresholdnumber of encoded data slices of the set to produce received encodeddata slices when the set of encoded data slices or a previous set ofencoded data slices is requested in accordance with a system maintainedaccess sequence (e.g., an allowed access sequence). Note that encodeddata slices may not be available for receiving when the encoded dataslices are not requested in accordance with the system maintained accesssequence (e.g., not sent from a dispersed storage (DS) unit). The methodcontinues at step 390 where the processing module dispersed storageerror decodes the received encoded data slices to produce recovereddecoded data.

The method continues at step 392 where the processing module determineswhether to exit the loop. The method repeats back to step 386 to repeatthe loop when the set of encoded data slices is not a last set of theplurality of sets of encoded data slices and when the request of the setof encoded data slices and a previous set of encoded data slices arerequested in accordance with the system maintained access sequence(e.g., in order of the system maintained access sequence). The methodbranches to step 396 to exit the loop when the set of encoded dataslices is the last set of the plurality of sets of encoded data slices.The method continues to step 394 where the process ends when theprocessing module determines to exit the loop when the set of encodeddata slices or the previous set of encoded data slices is not requestedin accordance with the system maintained access sequence. The methodcontinues at step 396 where the processing module combines the recovereddecoded data to produce a data file when the set of encoded data slicesis the last set of the plurality of sets of encoded data slices.

FIG. 24 is a flowchart illustrating an example of verifying a retrievalsequence. The method begins with step 400 where a processing moduledetects a data retrieval request regarding retrieval of data stored as aplurality of sets of encoded data slices in a dispersed storage network(DSN) memory. Such detecting may include receiving a slice retrievalindicator message from a DS unit, wherein the slice retrieval indicatormessage may include one or more of a user identifier (ID), a sourcename, a slice name, a timestamp, a data type, a dispersed storage (DS)processing unit ID, input access sequence information, a priorityindicator, a performance indicator, and a reliability indicator. Notethat the slice names and timestamps may include references to a previoustwo or more retrievals processed by a same DS processing unit for a sameuser. Further note that the two or more retrievals may indicate aportion of a retrieval sequence. Note that a set of encoded data slicesincludes at least one of encoded data slices of a data segment of aplurality of data segments of a data file and encoded data slices of theplurality of data segments having a common pillar number.

The method continues at step 402 where the processing module determinesa system maintained access sequence for retrieving the plurality of setsof encoded data slices based on the data retrieval request. Such asystem maintained access sequence includes at least one of a series ofordered slice names of the plurality of sets of slice names, a series ofordered segment identification codes, and a series of ordered pillaridentification codes. Such a determination may be based on at least oneof the data ID, a requester ID, a source name, a data type indicator, avault lookup, a predetermination, a command, a message, a DS processingunit ID, a priority indicator, a performance indicator, and areliability indicator.

The method continues at step 404 where the processing module detects aslice retrieval message for a set of encoded data slices of theplurality of sets of encoded data slices. The method continues at step406 where the processing module determines whether the set of encodeddata slices or a previous set of encoded data slices is requested inaccordance with the system maintained access sequence. Such adetermination may be based on determining whether the set of encodeddata slices or the previous set of encoded data slices is requested inaccordance with the system maintained access sequence, includingextracting temporal retrieval information (e.g., timestamps) of the setof encoded data slices and the previous set of encoded data slices,ordering the set of encoded data slices and the previous set of encodeddata slice in accordance with the temporal retrieval information toproduce an actual access sequence, and comparing the system maintainedaccess sequence with the actual access sequence. For example, theprocessing module determines that the set of encoded data slices or theprevious set of encoded data slices is requested in accordance with thesystem maintained access sequence when the system maintained accesssequence substantially includes the actual access sequence so far.

The method branches to step 410 when the processing module determinesthat the set of encoded data slices or the previous set of encoded dataslices is requested in accordance with the system maintained accesssequence. The method continues to step 408 when the processing moduledetermines that the set of encoded data slices or the previous set ofencoded data slices is not requested in accordance with the systemmaintained access sequence. The method continues and ends at step 408where the processing module sends a retrieval termination message to theDSN memory. Such sending of the retrieval termination message to the DSNmemory includes at least one of sending the retrieval terminationmessage to one or more DS units (e.g., those being utilized to retrievethe encoded data slices so far), sending the retrieval terminationmessage to a DS processing unit (e.g., a DS processing unit requestingretrieval of the data), and sending the retrieval termination message toa DS managing unit (e.g., to report an error of inappropriate access).

At step 410 the processing module determines whether the set is a lastset of the plurality of sets of encoded data slices. The method repeatsback to step 404 on the processing module determines that the set ofencoded data slices is not the last set of the plurality of sets ofencoded data slices and when the request of the set of encoded dataslices and the previous set of encoded data slices are retrieved inaccordance with the system maintained access sequence. The method endsat step 412 when the processing module determines that the set ofencoded data slices is the last set of the plurality of sets of encodeddata slices.

As may be used herein, the terms “substantially” and “approximately”provides an industry-accepted tolerance for its corresponding termand/or relativity between items. Such an industry-accepted toleranceranges from less than one percent to fifty percent and corresponds to,but is not limited to, component values, integrated circuit processvariations, temperature variations, rise and fall times, and/or thermalnoise. Such relativity between items ranges from a difference of a fewpercent to magnitude differences. As may also be used herein, theterm(s) “operably coupled to”, “coupled to”, and/or “coupling” includesdirect coupling between items and/or indirect coupling between items viaan intervening item (e.g., an item includes, but is not limited to, acomponent, an element, a circuit, and/or a module) where, for indirectcoupling, the intervening item does not modify the information of asignal but may adjust its current level, voltage level, and/or powerlevel. As may further be used herein, inferred coupling (i.e., where oneelement is coupled to another element by inference) includes direct andindirect coupling between two items in the same manner as “coupled to”.As may even further be used herein, the term “operable to” or “operablycoupled to” indicates that an item includes one or more of powerconnections, input(s), output(s), etc., to perform, when activated, oneor more its corresponding functions and may further include inferredcoupling to one or more other items. As may still further be usedherein, the term “associated with”, includes direct and/or indirectcoupling of separate items and/or one item being embedded within anotheritem. As may be used herein, the term “compares favorably”, indicatesthat a comparison between two or more items, signals, etc., provides adesired relationship. For example, when the desired relationship is thatsignal 1 has a greater magnitude than signal 2, a favorable comparisonmay be achieved when the magnitude of signal 1 is greater than that ofsignal 2 or when the magnitude of signal 2 is less than that of signal1.

The present invention has also been described above with the aid ofmethod steps illustrating the performance of specified functions andrelationships thereof. The boundaries and sequence of these functionalbuilding blocks and method steps have been arbitrarily defined hereinfor convenience of description. Alternate boundaries and sequences canbe defined so long as the specified functions and relationships areappropriately performed. Any such alternate boundaries or sequences arethus within the scope and spirit of the claimed invention.

The present invention has been described, at least in part, in terms ofone or more embodiments. An embodiment of the present invention is usedherein to illustrate the present invention, an aspect thereof, a featurethereof, a concept thereof, and/or an example thereof. A physicalembodiment of an apparatus, an article of manufacture, a machine, and/orof a process that embodies the present invention may include one or moreof the aspects, features, concepts, examples, etc. described withreference to one or more of the embodiments discussed herein.

The present invention has been described above with the aid offunctional building blocks illustrating the performance of certainsignificant functions. The boundaries of these functional buildingblocks have been arbitrarily defined for convenience of description.Alternate boundaries could be defined as long as the certain significantfunctions are appropriately performed. Similarly, flow diagram blocksmay also have been arbitrarily defined herein to illustrate certainsignificant functionality. To the extent used, the flow diagram blockboundaries and sequence could have been defined otherwise and stillperform the certain significant functionality. Such alternatedefinitions of both functional building blocks and flow diagram blocksand sequences are thus within the scope and spirit of the claimedinvention. One of average skill in the art will also recognize that thefunctional building blocks, and other illustrative blocks, modules andcomponents herein, can be implemented as illustrated or by discretecomponents, application specific integrated circuits, processorsexecuting appropriate software and the like or any combination thereof.

What is claimed is:
 1. A method for execution by a computing device, themethod comprises: identifying a storage unit of a set of storage unitswithin a dispersed storage system as being likely to fail; determiningan approach for minimizing rebuilding of encoded data slices stored onthe identified storage unit in an event of a failure of the identifiedstorage unit, wherein the approach is at least one approach option froma list of approach options, wherein the list of approach optionsincludes fostering new encoded data slices, replicating existing encodeddata slices, and re-dispersing existing encoded data slices;implementing the approach regarding the identified storage unit; andwhen the identified storage unit fails, retrieving the encoded dataslices that were stored on the identified storage unit based on theapproach.
 2. The method of claim 1, wherein the identifying the storageunit comprises: determining a detection of at least one of: amaintenance cycle; a network failure; an error message; a powerindicator; a weather indicator; an earthquake indicator; and anestimated future availability indicator.
 3. The method of claim 1,wherein the retrieving the encoded data slices further comprises: whenthe approach includes the fostering new encoded data slices: sending aretrieval command to a foster storage unit that is storing the newencoded data slices; and receiving the fostered encoded data slices. 4.The method of claim 1, wherein the retrieving the encoded data slicesfurther comprises: when the approach includes the replicating existingencoded data slices: sending a retrieval command to a replicationstorage unit that is storing at least one of the replicated existingencoded data slices; and receiving the at least one of the replicatedexisting encoded data slices.
 5. The method of claim 1, wherein theretrieving the encoded data slices further comprises: when the approachincludes the re-dispersed existing encoded data slices: sending aretrieval command to a set of re-dispersal storage units regarding are-dispersed existing encoded data slice of the re-dispersed existingencoded data slices; receiving a set of re-dispersed encoded data slicesfrom the set of re-dispersal storage units; and decoding, based onre-dispersal parameters, the set of re-dispersed encoded data slices toreproduce the re-dispersed existing encoded data slice.
 6. The method ofclaim 1 further comprises: when the approach includes the fostering newencoded data slices: identifying a foster storage unit; and instructingthe computing device to send the new encoded data slices to the fosterstorage unit.
 7. The method of claim 1 further comprises: when theapproach includes the replicating the existing encoded data slices:identifying a replicating storage unit; and instructing the identifiedstorage unit to send a copy of at least some of the encoded data slicesto the replicating storage unit.
 8. The method of claim 1 furthercomprises: when the approach includes the re-dispersing the existingencoded data slices: determining re-dispersal parameters; identifying aset of re-dispersal storage units; and instructing the identifiedstorage unit to: dispersed storage error encode, in accordance with there-dispersal parameters, one of the encoded data slices to createsub-slices; and send the sub-slices to the set of re-dispersal storageunits.
 9. A computing device comprises: an interface; memory; and aprocessing module operably coupled to the interface and the memory,wherein the processing module is operable to: identify a storage unit ofa set of storage units within a dispersed storage system as being likelyto fail; determine an approach for minimizing rebuilding of encoded dataslices stored on the identified storage unit in event of a failure ofthe identified storage unit, wherein the approach is at least oneapproach option from a list of approach options, wherein the list ofapproach options includes fostering new encoded data slices, replicatingexisting encoded data slices, and re-dispersing existing encoded dataslices; implement the approach regarding the identified storage unit;and when the identified storage unit fails, retrieve, via the interface,the encoded data slices that were stored on the identified storage unitbased on the approach.
 10. The computing device of claim 9, wherein theprocessing module in the identifying the storage unit further functionsto: determine a detection of at least one of: a maintenance cycle; anetwork failure; an error message; a power indicator; a weatherindicator; an earthquake indicator; and an estimated future availabilityindicator.
 11. The computing device of claim 9, wherein the processingmodule in the retrieving the encoded data slices functions to: when theapproach includes the fostering new encoded data slices: send aretrieval command to a foster storage unit that is storing the newencoded data slices; and receive the fostered encoded data slices. 12.The computing device of claim 9, wherein the processing module in theretrieving the encoded data slices functions to: when the approachincludes the replicating existing encoded data slices: send a retrievalcommand to a replication storage unit that is storing at least one ofthe replicated existing encoded data slices; and receive the at leastone of the replicated existing encoded data slices.
 13. The computingdevice of claim 9, wherein the processing module in the retrieving theencoded data slices functions to: when the approach includes there-dispersed existing encoded data slices: send a retrieval command to aset of re-dispersal storage units regarding a re-dispersed existingencoded data slice of the re-dispersed existing encoded data slices;receive a set of re-dispersed encoded data slices from the set ofre-dispersal storage units; and decode, based on re-dispersalparameters, the set of re-dispersed encoded data slices to reproduce there-dispersed existing encoded data slice.
 14. The computing device ofclaim 9, wherein the processing module is further operable to: when theapproach includes the fostering new encoded data slices: identify afoster storage unit; and instruct the computing device to send the newencoded data slices to the foster storage unit.
 15. The computing deviceof claim 9, wherein the processing module is further operable to: whenthe approach includes the replicating the existing encoded data slices:identify a replicating storage unit; and instruct the identified storageunit to send a copy of at least some of the encoded data slices to thereplicating storage unit.
 16. The computing device of claim 9, whereinthe processing module is further operable to: when the approach includesthe re-dispersing the existing encoded data slices: determinere-dispersal parameters; identify a set of re-dispersal storage units;and instruct the identified storage unit to: dispersed storage errorencode, in accordance with the re-dispersal parameters, one of theencoded data slices to create sub-slices; and send the sub-slices to theset of re-dispersal storage units.
 17. A computer readable storagedevice comprises: a first memory section for storing operationalinstructions that, when executed by a computing device, causes thecomputing device to: identify a storage unit of a set of storage unitswithin a dispersed storage system as being likely to fail; a secondmemory section for storing operational instructions that, when executedby the computing device, causes the computing device to: determine anapproach for minimizing rebuilding of encoded data slices stored on theidentified storage unit in event of a failure of the identified storageunit, wherein the approach is at least one approach option from a listof approach options, wherein the list of approach options includesfostering new encoded data slices, replicating existing encoded dataslices, and re-dispersing existing encoded data slices; and implementthe approach regarding the identified storage unit; and a third memorysection for storing operational instructions that, when executed by thecomputing device, causes the computing device to: when the identifiedstorage unit fails, retrieve, via an interface, the encoded data slicesthat were stored on the identified storage unit based on the approach.18. The computer readable storage device of claim 17, wherein the firstmemory section further stores operational instructions that, whenexecuted by the computing device, causes the computing device toidentify the storage unit by: determining a detection of at least oneof: a maintenance cycle; a network failure; an error message; a powerindicator; a weather indicator; an earthquake indicator; and anestimated future availability indicator.
 19. The computer readablestorage device of claim 17, wherein the third memory section furtherstores operational instructions that, when executed by the computingdevice, causes the computing device to retrieve the encoded data slicesby: when the approach includes the fostering new encoded data slices:sending a retrieval command to a foster storage unit that is storing thenew encoded data slices; and receiving the fostered encoded data slices.20. The computer readable storage device of claim 17, wherein the thirdmemory section further stores operational instructions that, whenexecuted by the computing device, causes the computing device toretrieve the encoded data slices by: when the approach includes thereplicating existing encoded data slices: sending a retrieval command toa replication storage unit that is storing at least one of thereplicated existing encoded data slices; and receiving the at least oneof the replicated existing encoded data slices.
 21. The computerreadable storage device of claim 17, wherein the third memory sectionfurther stores operational instructions that, when executed by thecomputing device, causes the computing device to retrieve the encodeddata slices by: when the approach includes the re-dispersed existingencoded data slices: sending a retrieval command to a set ofre-dispersal storage units regarding a re-dispersed existing encodeddata slice of the re-dispersed existing encoded data slices; receiving aset of re-dispersed encoded data slices from the set of re-dispersalstorage units; and decoding, based on re-dispersal parameters, the setof re-dispersed encoded data slices to reproduce the re-dispersedexisting encoded data slice.
 22. The computer readable storage device ofclaim 17 wherein the second memory section stores further operationalinstructions that, when executed by the computing device, causes thecomputing device to: when the approach includes the fostering newencoded data slices: identify a foster storage unit; and instruct thecomputing device to send the new encoded data slices to the fosterstorage unit.
 23. The computer readable storage device of claim 17wherein the second memory section stores further operationalinstructions that, when executed by the computing device, causes thecomputing device to: when the approach includes the replicating theexisting encoded data slices: identify a replicating storage unit; andinstruct the identified storage unit to send a copy of at least some ofthe encoded data slices to the replicating storage unit.
 24. Thecomputer readable storage device of claim 17 wherein the second memorysection stores further operational instructions that, when executed bythe computing device, causes the computing device to: when the approachincludes the re-dispersing the existing encoded data slices: determinere-dispersal parameters; identify a set of re-dispersal storage units;and instruct the identified storage unit to: dispersed storage errorencode, in accordance with the re-dispersal parameters, one of theencoded data slices to create sub-slices; and send the sub-slices to theset of re-dispersal storage units.